Calculate the mass of 12.044 × 10²⁵ molecules of oxygen (O₂).

Number of molecules of oxygen = 12.044 × 10²⁵ 

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