Which of the following equations follows the law of conservation of mass?

The reaction that has been following the law of conservation of mass has been reaction 1. Thus, option A is correct.

The law of conservation of mass has been given as the mass cannot be created nor be destroyed in a chemical reaction. The law of conservation of mass has equal weight of the reactants and the products.

The mass of following reactions can be given as:

124 g              =   124 g

Thus, the reaction follows the law of conservation of mass.

12g + 4(2)g   =   16g

20g = 16g

The reactant and product mass has not been equal, thus not follows the law of conservation of mass.

3(18)   = 3(2) + 3(32)

54g = 102g

The reactant and product mass has not been equal, thus not follows the law of conservation of mass.

2(23) + 36.5 = 58.5 g

81.5g = 58.5g

The reactant and product mass has not been equal, thus not follows the law of conservation of mass.

The reaction that has been following the law of conservation of mass has been reaction 1. Thus, option A is correct.

For more information about the law of conservation of mass, refer to the link:

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option A = C₂H₄ + 3O₂   →    2CO₂   +  2H₂O

Explanation:

Law of conservation of mass:

This law stated that mass can not be created or destroyed in chemical reaction. It just changed from one to another form.

For example:

C₂H₄   +   3O₂   →    2CO₂   +  2H₂O

28 g   + 96 g    =      88 g  +  36 g

    124  g           =      124 g

This reaction correctly hold the law of conservation of mass.

Other options:

C  + 4H₂  →   CH₄

12 g  + 8g  = 16 g

  20 g  =   16 g

This reaction do not hold the law of conservation of mass.

3H₂O  →   3H₂  +  3O₂

  54 g  =   6 g +  96 g

   54 g =   102 g

This reaction do not hold the law of conservation of mass.

2Na  +  Cl  →  NaCl

46 g  + 35.5 g  =   58.5 g

  81.5 g = 58.5 g

This reaction do not hold the law of conservation of mass.