What is the formula mass of nitric acid?

$H N {O}_{3}$; this has a molar mass of $\left(1.00794 + 14.01 + 3 \times 16\right)$ $g \cdot m o {l}^{-} 1$
Typically this is supplied as a 68-70% solution, with a concentration of approx. $15$ $m o l \cdot {L}^{-} 1$.