Question

name one periodic trend, and what is its trend?

Explanation:

One periodic trend is atomic radius. The trend of atomic radius is that it generally decreases across a period (from left to right in the periodic table) because the effective nuclear charge increases, pulling the electrons closer to the nucleus. Down a group (top to bottom), atomic radius increases as new electron shells are added, increasing the distance between the nucleus and the outermost electrons. (Note: Assuming "it's trend" is a typo for "its trend".)

Answer:

One periodic trend: Atomic radius. Its trend: Generally decreases across a period (left - right) and increases down a group (top - bottom).