NickFit saidIt can't be illegal to ask for sexual orientation on a job application in the UK, because I applied for a job with the police force last year where they asked that. There is also the option to refuse answering though.
I think that application form was just badly designed, but it does look as though it's implying your orientation is linked to disability.
P.s. I answered that question honestly, and was offered the job. I turned it down though, in the end.
It's definitley illegal in the UK, as it is in Ireland. Same goes for race, gender age etc. In Ireland it's covered under the Employment Equality Act 1998.
You can aske the question, but you leave yoursefl wide open to claims and the burden of proof rests with the respondent to the claim (i.e. the employer)
To such a degree, that if you even write down someones age for instance on your notepad while interviewing them, they can request that sheet of paper and claim under the equality act that it was for that reason they disn't succeed in the interview.
I would be very surprised if the same isn't true in the USA.