It depends on if you mean "what's the probability of a coin landing heads" or if you mean "what's the probability a coin tossed 4 times will land heads 2 times?

It depends on if you mean "what's the probability of a coin landing heads" or if you mean "what's the probability a coin tossed 4 times will land heads 2 times?" The first is 1/2 = 2/4.