Explain the following:

Metallic character of elements decreases from left to right in a period while it increases in moving down a group.

On moving across a period from left to right, nuclear pull increases due to the increase in atomic number and thus the atomic size decreases. Hence, elements cannot lose electrons easily. Therefore, the metallic character decreases across a period.
On moving down the group, the atomic size increases and the nuclear charge also increases. The effect of an increased atomic size is greater as compared to the increased nuclear charge. Therefore, tendency to lose electron increases and elements can lose electrons easily. Thus, metallic character of elements increases in moving down a group.