Which diagram would it be?

2CH4 > 3H2 + C2H2

Explanation:

The law of conservation of mass states that atoms can neither be created nor destroyed in a chemical reaction.

The implication of this law is that the number of atoms of each element on the reactant side must be equal to the number of atoms of each element on the product side.

This law is only obeyed by the reaction, 2CH4 > 3H2 + C2H2

There were eight atoms of H on the left hand side as well as the right and side of the reaction equation. There were two atoms of C on both the left and right hand sides of the reaction equation respectively. Hence, the law was obeyed here.

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