Travelling in Serbia you will meet Types C and F sockets, fed with 230 V at 50 Hz. No surprises on voltage: Serbia runs at 230 V, the same range as at home in the UK.
The same socket system is used in Türkiye, Sweden, Germany and Russia, so one adapter covers all of them. Watch out when moving on: the United Kingdom, Gibraltar and Malta use a completely different system. In Europe, 31 of 50 recorded destinations use exactly this combination.
Protective earth
Grounded and ungrounded sockets may occur
Not every socket in Serbia is earthed: Type F yes, Type C no. Class I appliances belong in an earthed outlet.