Atomic size generally
a. increases as you move from left to right across a period
b. decreases as you move from top to bottom within a group
c. remains constant within a period
d. decreases as you move from left to right across a period

Atomic size generally

D. decreases as you move from left to right across a period

elements are classified into periods based on the number of energy shells.

elements that have the same number of energy shells fall into the same period.

as you go from left to right across a period, the atomic number increases. Atomic number is the number of protons. In ground state atoms the protons and electrons are the same.

so as you go across a period, the number of protons and electrons increase.

protons are positively charged and located in the nucleus. Electrons are negatively charged and are in energy shells. With higher number of protons in the nucleus, higher the positive charge in the nucleus. Then the force of attraction from the nucleus towards the electrons in the energy shells are higher.It will pull the energy shells more towards the nucleus making the atomic size smaller.

therefore atomic size decreases as you move from left to right across a period

10 years is the answer