He is a man of mellow temper.

excitable
hot
irrational
fickle

The correct answer is A. excitable.

A man of mellow temper is not excitable. He is not easily angered or excited. He is calm and level-headed. He is not hot-tempered or irrational. He is not fickle or easily swayed by his emotions.

Excitable means easily excited or aroused. Hot-tempered means easily angered. Irrational means not based on or in accordance with reason or logic. Fickle means likely to change one’s mind or feelings easily.