molarity is defined as the number of moles of solute in 1 L of solution
molar mass of Ni(NO₃)₂ - 182.7 g/mol
number of moles of Ni(NO₃)₂ - 5.80 g/ 182.7 g/mol = 0.0317 mol
number of moles in 500 mL - 0.0317 mol
therefore number of moles in 1000 mL - 0.0317 mol / 500 mL x 1000 mL/L
molarity of the solution is - 0.0634 M