The procedure calls for 2.0 mL of concentrated nitric acid. How many moles is this?

Commercial HNO3 is 68-70% HNO3 (w/w). The 68% stuff is 15.2 M so mols = M x L = 15.2 M x 0.002 L = mols HNO3 in 2 mL of 68% HNO3.