Question

why hydrogen is common in all acid ?​

Answer 1

it is proton donor ...

I think it is CORRECT

....

Answer 2

Here's the answer-

There are different categories of Acids like -

Bronsted Acid - in which H(+) is a donor.

Arrhenius Acid - which dissociates in aqueous solutions to give H(+)

Lewis acid - which can accept a pair of electron in its vacant orbitals.

Now , we can not really say that hydrogen is common in all acids like in Lewis acids like BF3

But yes in Arrhenius Acid and Bronsted acid , all acids must have Hydrogen so as to release H(+) i.e. a proton to satisfy themselves as being acid and can donate their H(+) to other species.

Hope This helped.