Answer: 4.01x 10 ²² molecules HNO3
Explanation: Solution attached:
Convert mass of HNO3 to moles using its molar mass.
Convert moles of HNO3 to molecules using the Avogadro's number
4.20 g HNO3 x 1 mole HNO3 / 63 g HNO3 x 6.022x10²³ molecules HNO3 / 1 mole HNO3
= 4.0X 10 ²² molecules HNO3
