The reason for the decrease in the atomic size of elements across a period is that

A Nuclear charge increases while the outermost electrons are drawn closer to the nucleus
B Nuclear charge decreases while the outermost electrons are drawn closer to the nucleus
C Valence electrons increase across the period while the valence shell remains constant
D Nuclear charge decreases while the distance of the valence shell from the nucleus is increasing

Correct Answer: Option A

Explanation:
This is caused by the increase in the number of protons and electrons across a period.