Question

1. choose the best answer.

which of the following equations represents a decomposition reaction?
8fe + s8 → 8fes
mgco₃(s) → mgo(s) + co₂(s)
2no + o₂ → 2no₂
2co(g) + o₂(g) → 2co₂(g)

Explanation:

Step1: Recall decomposition reaction

A decomposition reaction is when one compound breaks into two or more simpler substances (elements or compounds). The general form is \( AB
ightarrow A + B \).

Step2: Analyze each option

• Option 1: \( 8\text{Fe} + \text{S}_8

ightarrow 8\text{FeS} \) – This is a combination (synthesis) reaction (two substances combine to form one), not decomposition.

• Option 2: \( \text{MgCO}_3(s)

ightarrow \text{MgO}(s) + \text{CO}_2(s) \) – One compound (\( \text{MgCO}_3 \)) breaks into two simpler substances (\( \text{MgO} \) and \( \text{CO}_2 \)), fits decomposition.

• Option 3: \( 2\text{NO} + \text{O}_2

ightarrow 2\text{NO}_2 \) – Combination reaction (two reactants form one product).

• Option 4: \( 2\text{CO}(g) + \text{O}_2(g)

ightarrow 2\text{CO}_2(g) \) – Combination reaction (reactants combine to form a product).

Answer:

\( \text{MgCO}_3(s)
ightarrow \text{MgO}(s) + \text{CO}_2(s) \) (the second option)