You mix 15g of water with 10 grams of sodium chloride. After the reaction occurs, how many grams of your new substance do you have?

A) 15g
B) 25g
C) 20g
D) not enough information

B) 25g

Explanation:

Every reaction must follow the law of conservation of mass.

Law of conservation of mass:

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

Explanation:

This law was given by French chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

For example:

In given photosynthesis reaction:

6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂

there are six carbon atoms, eighteen oxygen atoms and twelve hydrogen atoms on the both side of equation so this reaction followed the law of conservation of mass.

In given example:

Water + sodium chloride   →   Product

15 g   +      10 gram       =              25 g

25 g           =      25 g

catya your not at all which answer i've seen you do this on another question!