Assertion (A) : Following is a balanced chemical equation for the action of steam on iron : 3Fe + 4H₂O → Fe₃O₄ + 4H₂
Reason (R): The law of conservation of mass holds good for a chemical equation.

Solution:
Both Assertion and Reason are true, but reason is not the correct explanation of Assertion.

(A) 3Fe + 4H₂O $\stackrel{}{\to }$ Fe₃O₄ + 4H₂
​​​​​​3 ​Fe atoms,8 H atoms, and 4 O atoms are balanced on both sides.
(B) Atomic mass of Fe is 56u, the molar mass of H₂O is 18u, the molar mass of Fe₃O₄ is 232u and H₂​ is 2u​​​​​​.
Total mass of reactants = 3(56) + 4(18) = 240u
Total mass of products = 232 + 4(2) = 240u

Since,mass of reactants = mass of products (Law of Conservation of Mass holds good)