Answer 1

12.044 × 10²⁵ molecules of oxygen

Mass of 6.022 × 10²³ molecules of oxygen = 32g

Mass of one molecule of oxygen = 32 / 6.022 × 10²³ = 5.3 × 10⁻²³g

Mass of 12.044 × 10²⁵ molecules of oxygen = 5.3 

10⁻²³ × 12.044 × 10²⁵ g = 6400g or 6.4kg

Hence, the mass of 12.044 × 10²⁵ molecules of oxygen is 6.4kg.