There are 18 vertical columns in the modern periodic table and these are known as groups.

i) Genetics is the mechanism by which variations are created and inherited.

ii) Evolution is used for studying the development of new types of organisms from the existing ones. 

Two ways to save this resource are:

i) Turning-off the taps when not in use.

ii) Frequent checking for the leakage of water pipelines, and getting them repaired. 

Vegetative propagation is an asexual mode of reproduction.

Advantages of vegetative propagation:

Only one parent is required, which eliminates the need for special mechanisms (pollination).

All plants produced are genetically similar enough to the parent plant to have all its characteristics hence genetic characteristic of the parent plant can be preserved.

Plants that do not produce seeds can be propagated by this method. For example Sugar-cane, Potato, etc.

Vegetative propagation is a cheaper, easier and rapid method of propagation in plants than growing them from their seeds. 

The figure drawn below illustrates the path of reflected ray corresponding to an incident ray which is directed parallel to the principal axis of a convex mirror.