Question

1. Which of the following is a displacement reaction? (a) MgCO3 - → MgO + CO2 (b) 2Na + 2H20 - → 2NaOH + H2 (c) 2H2 + O2 → 2H2O Heat (d) 2Pb (NO3)2 2PbO + 4NO2 + O2 Answer/ Explanation​

Answer 1

In this quesyion option B is a example of displacement reaction

BEACUSE

Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions. Example : Reaction of iron nails with copper sulphate solution.

Answer 2

Among the following, the displacement reaction is $\[2Na + 2{H_2}O \to 2NaOH + {H_2}\]$. Thus, the correct option is (b).

Explanation:

• A displacement reaction is a reaction in which a more reactive element displaces another less reactive element from its compound to form a new compound.
• In the reaction, $\[2Na + 2{H_2}O \to 2NaOH + {H_2}\]$, sodium is more reactive than hydrogen according to the reactivity series, therefore, it displaces hydrogen from water to form sodium hydroxide.  
• Thus, the reaction is a displacement reaction.
• In the reaction, $\[MgC{O_3} \to MgO + C{O_2}\]$, magnesium carbonate breaks into magnesium oxide and carbon dioxide. Therefore, it is a decomposition reaction.
• In the reaction, $\[2{H_2} + {O_2} \to 2{H_2}O + Heat\]$, hydrogen and oxygen combine together to form water. Thus, it is a combination reaction.
• In the reaction, $\[2Pb{(N{O_3})_2} \to 2PbO + 4N{O_2} + {O_2}\]$, lead nitrate decomposes to form lead (II) oxide, nitrogen dioxide and oxygen. Thus, it is a decomposition reaction.