That information is unnecessary.

That information is completely unnecessary.

Alkali metals are very reactive chemically.

This water has high alkalinity, so it is gentle on the skin.

He thinks that war is a necessary evil.

His body showed a rejection reaction to the transplanted organ.

His single word triggered a chain reaction, and everything changed.

She overreacted to his words.

Nuclear reactions are used for mass production of energy.

I was surprised by his overreaction.