What is the reciprocal of 2?

$\frac{1}{2}$.
Reciprocal means to "flip the fraction". So $2$ is basically $\frac{2}{1}$ ($2$ over $1$) if you write it as a fraction.
So if you simply flip $\frac{2}{1}$, it is $\frac{1}{2}$, which can also be $0.5$