Question 1:

The correct answer is C.

Explanation:

• Group 1 metals (e.g., Na, K) lose 1 electron to achieve a noble gas configuration → 1+ charge.

• Group 2 metals (e.g., Mg, Ca) lose 2 electrons → 2+ charge.

• Group 6 non-metals (e.g., O, S) gain 2 electrons to achieve a noble gas configuration → 2- charge.

• Group 7 non-metals (e.g., F, Cl) gain 1 electron → 1- charge.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 2:

The correct answer is A.

Explanation:

These are the standard formulae for common polyatomic ions that you are expected to memorize in chemistry:

• Hydroxide: OH⁻ (1 oxygen, 1 hydrogen, –1 charge)

• Carbonate: CO₃²⁻ (1 carbon, 3 oxygens, –2 charge)

• Sulfate: SO₄²⁻ (1 sulfur, 4 oxygens, –2 charge)

• Nitrate: NO₃⁻ (1 nitrogen, 3 oxygens, –1 charge)

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 3:

The correct answer is B. CaCl₂.

Explanation:

• Calcium is in Group 2, so it forms ions with a 2+ charge: Ca²⁺.

• Chlorine is in Group 7, so it forms ions with a 1− charge: Cl⁻.

• To form a neutral compound, the total positive charge must balance the total negative charge. One Ca²⁺ ion (+2) needs two Cl⁻ ions (−1 each) to balance the charge:
  Ca²⁺ + 2Cl⁻ → CaCl₂

Why the other options are incorrect:

• A. CaCl – This would imply Ca⁺ and Cl⁻, but calcium forms Ca²⁺, not Ca⁺. The charges would not balance.

• C. Ca₂Cl – This would give a total charge of +4 from two Ca²⁺ ions and −1 from one Cl⁻, which does not balance.

• D. Ca₇Cl₂ – This is completely incorrect and does not reflect the valencies of calcium and chlorine.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 4:

The correct answer is D. Na₂CO₃.

Explanation:

• Sodium is in Group 1, so it forms ions with a 1+ charge: Na⁺.

• Carbonate is a polyatomic ion with the formula CO₃²⁻ (as given in the previous question).

• To form a neutral compound, the total positive charge must balance the total negative charge. One CO₃²⁻ ion has a 2− charge, so it needs two Na⁺ ions (+1 each) to balance:
  Na⁺ + Na⁺ + CO₃²⁻ → Na₂CO₃

Why the other options are incorrect:

• A. Na₃CO – This has the wrong formula for carbonate (should be CO₃, not CO) and the charges do not balance correctly.

• B. NaCO₃ – This would imply only one Na⁺ (+1) balancing a CO₃²⁻ (−2), which does not give a neutral compound.

• C. Na(CO₃)₂ – This would give a total charge of +1 from sodium and −4 from two carbonate ions, which does not balance. Also, the formula is not written in the simplest ratio.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 5:

The correct answer is C. Pb(OH)₂.

Explanation:

• Lead(II) indicates that lead forms ions with a 2+ charge: Pb²⁺.

• Hydroxide is a polyatomic ion with the formula OH⁻ (as given in the previous question).

• To form a neutral compound, the total positive charge must balance the total negative charge. One Pb²⁺ ion (+2) needs two OH⁻ ions (−1 each) to balance:
  Pb²⁺ + 2OH⁻ → Pb(OH)₂

(The parentheses around OH are used to show that there are two separate hydroxide ions, not a single group with a subscript 2 on hydrogen.)

Why the other options are incorrect:

• A. PbOH – This would imply Pb⁺ and OH⁻, but lead(II) forms Pb²⁺, not Pb⁺. The charges would not balance.

• B. Pb₂OH – This would give a total charge of +4 from two Pb²⁺ ions and −1 from one OH⁻, which does not balance.

• D. PbOH₂ – This is incorrectly written. It suggests two hydrogen atoms attached to a single oxygen (which is not the hydroxide ion), rather than two separate hydroxide ions. The correct notation for two hydroxide ions is (OH)₂, not OH₂.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 6:

The correct answer is C. H⁺ from acids and OH⁻ from alkalis.

Explanation:

• Acids produce hydrogen ions (H⁺) in aqueous solution.

• Alkalis (soluble bases) produce hydroxide ions (OH⁻) in aqueous solution.

• In a neutralization reaction, the H⁺ ions from the acid and the OH⁻ ions from the alkali combine to form water:
  H⁺ + OH⁻ → H₂O

Why the other options are incorrect:

• A. The ions are reversed—acids produce H⁺, not OH⁻, and alkalis produce OH⁻, not H⁺.

• B. Both ions are incorrect. Acids produce H⁺ (not OH₂⁻), and alkalis produce OH⁻ (not H₂⁺). Also, these formulae do not represent real stable ions.

• D. While the acid ion (H⁺) is correct, the alkali ion is wrong. Alkalis produce OH⁻, not OH₂⁻.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 7:

The correct answer is A. CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g).

Explanation:

• CaCO₃ (s) – Marble chips are a solid.

• HCl (aq) – Hydrochloric acid is always in aqueous solution (dissolved in water).

• CaCl₂ (aq) – Calcium chloride is soluble in water and remains dissolved as ions in the solution.

• H₂O (l) – Water is produced as a liquid.

• CO₂ (g) – Carbon dioxide is given off as a gas.

Why the other options are incorrect:

• B. CaCl₂ is not a liquid under these conditions—it is dissolved in water, so it should be (aq), not (l).

• C. HCl is an aqueous solution, not a pure liquid (l). Also, CaCl₂ should be (aq), not (l).

• D. HCl should be (aq), not (l), because hydrochloric acid is always in solution. Also, H₂O is a liquid (l), not aqueous (aq)—"(aq)" is used for dissolved substances, not for the solvent itself.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 8:

The balanced chemical equation is:

Mg + 2HCl → MgCl₂ + H₂

Explanation:

To balance the equation, we need the same number of each type of atom on both sides.

1. Magnesium (Mg): 1 atom on both sides → already balanced.

2. Chlorine (Cl): On the right, MgCl₂ has 2 chlorine atoms, so we need 2 HCl on the left to provide 2 chlorine atoms.

3. Hydrogen (H): With 2 HCl on the left, we have 2 hydrogen atoms. On the right, H₂ has exactly 2 hydrogen atoms → balanced.

So the coefficients are:

Final balanced equation:
1Mg + 2HCl → 1MgCl₂ + 1H₂
(or simply Mg + 2HCl → MgCl₂ + H₂).

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 9:

The balanced chemical equation is:

CH₄ + 2O₂ → CO₂ + 2H₂O

Explanation:

To balance the equation, we need the same number of each type of atom on both sides.

1. Carbon (C): 1 atom on both sides → already balanced.

2. Hydrogen (H): On the left, CH₄ has 4 hydrogen atoms. On the right, H₂O has 2 hydrogen atoms per molecule, so we need 2 H₂O to give 4 hydrogen atoms.

3. Oxygen (O): On the right, we now have 2 oxygen atoms from CO₂ and 2 oxygen atoms from 2H₂O (since 2 × 1 = 2), giving a total of 4 oxygen atoms. On the left, O₂ has 2 oxygen atoms per molecule, so we need 2 O₂ to give 4 oxygen atoms.

So the coefficients are:

Final balanced equation:
1CH₄ + 2O₂ → 1CO₂ + 2H₂O
(or simply CH₄ + 2O₂ → CO₂ + 2H₂O).

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 10:

The balanced chemical equation is:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Explanation:

To balance the equation, we need the same number of each type of atom on both sides.

1. Iron (Fe): On the left, Fe₂O₃ has 2 iron atoms, so we need 2 Fe on the right.

2. Oxygen (O): On the left, Fe₂O₃ has 3 oxygen atoms. Each CO molecule has 1 oxygen atom, and each CO₂ molecule has 2 oxygen atoms. To balance oxygen, we need the total oxygen on the right to equal that on the left.

3. Carbon (C): The number of CO molecules on the left must equal the number of CO₂ molecules on the right (since each has 1 carbon atom).

Let the coefficient of CO and CO₂ be x. Then:

• Oxygen on the left = 3 (from Fe₂O₃) + x (from CO)

• Oxygen on the right = 2x (from CO₂)

Set them equal:
3 + x = 2x → x = 3

So we need 3 CO and 3 CO₂.

Now check:

• Fe: 2 on left (Fe₂O₃), 2 on right (2Fe) ✓

• C: 3 on left (3CO), 3 on right (3CO₂) ✓

• O: 3 (from Fe₂O₃) + 3 (from 3CO) = 6 on left; 3 × 2 = 6 on right (from 3CO₂) ✓

So the coefficients are:

Final balanced equation:
Fe₂O₃ + 3CO → 2Fe + 3CO₂

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.