Question

An atom is $10$ times heavier than $\frac{1}{12}$th of mass of a carbon atom ($C-12$) The mass of the atom in amu is ?

• A. $10$
• B. $120$
• C. $1.2$
• D. $12$

Answer 1

Answer: (A)

$10$

By definition,

$1$ $amu={\left(\frac{1}{12}\right)}^{th}$ of mass of $C-12$

$\therefore$ Mass of atom which is $10$ times heavier than ${\left(\frac{1}{12}\right)}^{th}$ of mass of $C-12$ atom $=10[massof{\left(\frac{1}{12}\right)}^{th}C-12]$

$=10[1$ $amu]$

$=10$ $amu$

$1$ $mole$ of $CO=6.023\times {10}^{23}$ particles of CO

$6.023\times {10}^{23}$ atoms of $C$ contains $6.023\times {10}^{23}$ atoms of $O$.

Similarly, $6.023\times {10}^{24}$ atoms of $C$ contains $6.023\times {10}^{24}$ atoms of $O$

Now oxygen is diatomic

$10$ $g-$ atom $=\frac{1}{2}$ ($10$ $g$ molecule of $O_2$) $=5$ $g$ molecule of $O_2$