How can you show the conservation of mass when making a physical mixture? A.

Show that the total of the masses of the starting substances equals the mass of the mixture.

B.

Show that the total of the masses of the starting substances is greater than the mass of the mixture.

C.

Show that the mass of some of the substances changes during mixing.

D.

Show that the mass of the mixture depends on how quickly the substances are combined.
THERE IS MORE THAN ONE ANSWER

A. Show that the total of the masses of the starting substances equals the mass of the mixture.

Explanation:

Law of conservation of mass:

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

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 a similar way if we have mixture of sugar and sand the total weight of mixture is equal to the weight of reactants.

sand + sugar + water    → mixture

     10g+5g+20 g           =   35 g

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

the dissolution of polymer can be thermodynamically described in 2 steps.