Is it a fire risk/hazard, if we do not connect electric bulbs to all bulb holders, say above wash basin, but use some bulbs and rest of the bulb holders are empty and use as is.
Absolutely not. But there is a shock hazard if some nitwit should stick a finger into an empty socket, so it is well to leave dead bulbs screwed in if you don't care to replace them with good ones.
There is not risk unless you have people who put their fingers in the socket. You might consider keeping burned out light bulbs for some locations or buying the adaptors that let you plug into a light socket (screw in with two slots for the plug) but just to fill the socket in this case.
I agree with using burnt out bulbs or not completely screwing the bulb in. I would think a burn bulb would look better than an empty socket. If you chose not to use any bulbs in it, at least cover the socket with black electrical tape so that some idiot doesn't stick their finger in it.
No fire risk or hazard except if sticking something in the empty live socket.
Don't be splashing any water up near there, or puttin' your fingers in those sockets! Okay, look, just put some burned out or low voltage bulbs in the one's you don't want to use. Then you can count how many people come over, use your bathroom, and then tell you, you have a burned out bulb above the sink. LOL
