Arrange the following in the order of increasing mass. (Atomic mass of $\text{O}=16\text{u},\text{\hspace{0.17em}\hspace{0.17em}Cu}=63\text{u},\text{\hspace{0.17em}\hspace{0.17em}N}=14\text{u}$ )

I) One atom of oxygen    II) one atom of nitrogen    III)  $1\times {10}^{-10}$  mole of oxygen gas    IV) $1\times {10}^{-10}$ mole of copper

Single atom of nitrogen has the mass 14 u but single atom of oxygen has 16u as mass. Hence, II < I. In the similar way, $1\times {10}^{-10}$ mol of copper has greater atomic mass than $1\times {10}^{-10}$ mol of oxygen. Hence, III  < IV.

Therefore, overall increasing order of atomic mass is $\text{II}<\text{I}<\text{III}<\text{IV}$