Why was the hydrogen atom able to attach to the oxygen atom but not the chlorine atom???

Chlorine has a higher electronegativity, but as it has a large atomic radius the electron density is spread out over a large area. This means that the electron density is too low to form proper hydrogen bonds, and will only be attracted via dipole-dipole attraction.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current