Question

How many hydrogen atoms are attached to each carbon adjacent to a double bond?

Answer 1

In double bond there are two hydrogen atoms attached to each carbon .
As carbon has atomic no.6 and other most shell has4 electrons .It needs more 4 elections to be stable .

Answer 2

Carbon is a non metal with valency - 4- TetraValent.

In double bonds :
For example : C2H4 --- ETHENE

  H - C = C - H
        I      I
       H     H

SO , each carbon atom present in double bond will have 2 hydrogen atoms .

So total number of hydrogen atoms - 4