What do you call the trends that decreases from left to right across a period?

The trends which decreases from left to right in a periodic table are atomic radius and metallic character.

Explanation:

ATOMIC RADIUS:

This is caused by the increase in number of electron and proton.As one proton has greater effect than one electron thus electrons are pulled towards the nucleus resulting in smaller radius.

METALLIC CHARACTER :

This is caused by the decrease in atomic radius that allows the outer electrons to ionize more readily.