Question

on the periodic table, atomic mass
a. increases up a group.
b. decreases down a group.
c. decreases across a period from left to right.
d. increases across a period from left to right.

Explanation:

Atomic mass is the mass of an atom, mainly determined by protons and neutrons. As we move across a period from left - right, the number of protons and neutrons generally increases, leading to an increase in atomic mass. Down a group, atomic mass increases as well.

Answer:

D. increases across a period from left to right