Why is there no p-block in period 1?

Hint: According to the periodic law, the properties of the elements are a
the periodic function of their atomic weights. In the periodic table of the elements, the horizontal rows are called periods. The vertical columns are called groups.

Complete Step by Step Solution:
Elements possessing identical outer electron configurations in their atoms are organised in vertical columns called groups or families.
There are a total of seven periods.
The period number indicates the highest principal quantum number (n) of the elements in the period.
The first period contains two elements Hydrogen and Helium.
The atomic number of Hydrogen is 1.
It has one electron present in 1s orbital.
So, its principal quantum number or n is 1.
The atomic number of Helium is 2.
It has two electrons present in the 1s orbital.
So, its principal quantum number or n is 1.
Hence, there are two elements in the first period.
P-block elements starting from Boron have principal quantum numbers like 2,3,4,5 and 6.
Hence, they do not lie in the first period but in the second, third, fourth, fifth, and sixth periods.

Additional Information: The following periods comprises 8, 8, 18, 18 and 32 elements, respectively.
In this form of the Periodic Table, 14 elements of both the sixth and seventh periods (lanthanides
and actinoids, respectively) are positioned in distinct groups at the bottom.

Note: As the period depicts the highest principal quantum number of an element. So, the first period represents n=1. Only two elements are there that satisfy this condition and therefore, are placed in the first period.