How can you distinguish a from b?

The question is an illustration of physical and chemical properties.

To distinguish A from B, you simply observe their physical and chemical properties.

When taking note of physical changes, you simply observe how the form of the substance changes.

For instance, when substance A changes from liquid to solid, then substance A has undergone a physical change.

However, the chemical change to observe includes the formation of a new substance.

For instance, when a new substance (say B1) is formed from substance B, then you know that substance B has undergone a chemical change.

Hence, to distinguish between A and B, you have to find out their physical and chemical properties.

Read more about physical and chemical properties at:

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adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

explanation:

the answer to your question is c