pmf for coin toss

I am currently studying Statistical Inference class on Coursera. In one of the assignments, the following question comes up.

Let $$x=0$$ represent a 'heads' outcome and $$x=1$$ represent a 'tails' outcome of a coin toss. If $$p$$ is the probability of 'heads' which of the following represents the PMF of the coin toss? The variable x is either 0 (heads) or 1 (tails).

1: $$p^{1-x}(1-p)^x$$

2: $$p^x(1-p)^{1-x}$$

while solving it gave hint to choose option when head exponent is 1 so correct option was 1

if it said p is probability of tail which following represent the PMF of the coin toss will answer change

pmf ---- is it for independent event only

PMF of the coin toss means $$P_X(x) = P(X = x)$$. Note that capitals are always used for the random variables and small characters are specific values. There are only two possible values for $$X$$, i.e $$0, 1$$. So, $$P_X(0)=P(X=0)$$ which is $$p$$ by definition. So, $$P_X(1)=P(X=1)$$ should be $$1-p$$.
So, the function you'll have should satisfy these conditions, and that option is $$1$$, as in the hint of the question. You only need to substitute $$x = 0$$ and $$x = 1$$ to see if it's true.