Learn Russian: Разве это правда, а не просто слух? - Is it really the truth, and not just a rumor?

Adding разве turns a simple yes/no question into one that expresses doubt or surprise. The speaker is essentially saying, 'I thought it was just a rumor, are you telling me it is actually true?' It translates perfectly to 'Is it really...?' in this context.

Could we use неужели instead of разве in this sentence?

Yes, but there is a slight difference in tone. Неужели expresses a stronger, more emotional astonishment or shock. Разве is a bit milder and often shows that your previous assumption is being challenged, which fits perfectly with contrasting the truth against a rumor here.

Why do we use а for 'and' here instead of и?

А is used because we are setting up a direct contrast between two things: it is this (правда), and not that (не просто слух). When you have a 'not X, but Y' or 'X, and not Y' structure, Russian almost always uses а to show that contrast.

Does слух only mean 'rumor'?

It means 'rumor' in this context, but its literal and primary meaning is the physical sense of 'hearing'. Rumors are things you hear, which is why the same word is used for both! You will also frequently see it in the plural, слухи, to mean 'gossip' or 'rumors'.