Question

How to determine the number of valence electrons in an atom using the periodic table?

Answer 1

group number of a element determines the valency of elements, moving across the group the valency remains the same while moving down a period valency increases with increase in group number of a element

Answer 2

We can determine the valence electrons by looking periodic table as the group number of an atom n valence electrons r same. So it's Done by seeing at group number.
For example =carbon is in group 4. Hence valence electrons is also 4.
Hope it helps u dear