Question

Assertion :Atomic size decreases across period but increases down a group of the periodic table. Reason: Moving from left to right across a period, electrons are added one at a time to the outer energy shell. Electrons within a shell cannot shield each other from the attraction to protons, while moving down a group in the periodic table, the number of electrons and filled electron shells increases.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

In the same period, electrons are filled in same shell.

So, they are not able to screne each other. Thus the nuclear charge as well as effective nuclear charge increases. Thus the radius decreases.

In the group, however new shells are added and thus the radius increases.

Thus the assertion and Reason are true and reason explains the assertion.