Which one is the correct graph for $u[2-n]$? $u[n]$ is the unit step function in discrete form. I want to know which one of the following two is the correct waveshape for $u[2-n]$, where $k$ is a constant.

What's the answer? The top one is $u[n]$, the unit step function. So, what's the graph for $u[2-n]$, middle or bottom?
HINT: For which value of $n$ does the argument of $u[2-n]$ become zero? That's where the step occurs. For which values of $n$ is the argument non-negative? That's where your unit step equals $1$. If you think about it for a minute, it should become really easy.