In general, the rate of a reaction can be increased by
1. all of these
2. increasing the concentration of reactants.
3. increasing the temperature.
4. adding an appropriate catalyst.

1. All of these

Explanation:

The rate of a reaction depends on following factors:

1. increasing the concentration of reactants: means there is more particles of reactants per unit volume.Thus more particles can collide and hence the rate of reaction increases.

2. increasing the temperature- the particles move faster and undergo more collision which leads to an increase in the rate of the reaction.

3.adding an appropriate catalyst: addition of catalyst lowers the activation energy and thus more reactants can cross the energy barrier. Thus it leads to formation of more products hence an increase in the reaction rate.

Thus the rate of a reaction can be increased by  all of these.

the answer is c.the valence of the atoms combine .