To establish the formula for mercury(II) nitrate, we need to determine the charges of the mercury and nitrate ions and combine them in a way that results in a neutral compound.

Mercury(II) ion has a charge of 2+ (Hg2+).

Nitrate ion has a charge of 1- (NO3-).

To achieve a neutral compound, we need two nitrate ions to balance the charge of the mercury(II) ion.

So, the formula for mercury(II) nitrate is Hg(NO3)2.