Which one of the following is an example of a decomposition reaction?

Answer : The correct example of a decomposition reaction is, (A)

Explanation :

Decomposition reaction : It is defined as the reaction in which the the larger molecule decomposes to give two or more smaller molecules.

(A) The given balanced chemical reaction is,

This reaction is a decomposition reaction in which the the larger molecule calcium carbonate decomposes to give two or more smaller molecules as calcium oxide and carbon dioxide.

(B) The given balanced chemical reaction is,

This reaction is a synthesis reaction where multiple substances or reactants combine to form a single product.

(C) The given balanced chemical reaction is,

This reaction is a synthesis reaction in which the more reactive element replace the less reactive element.

(D) The given balanced chemical reaction is,

This reaction is a synthesis reaction in which the more reactive element replace the less reactive element.

Hence, the correct example of a decomposition reaction is, (A)

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.