The equivalent mass of a certain bivalent metal is $20$. The molecular mass of its anhydrous chloride is

Write about Formula Mass.

An alloy of metals $X$ and $Y$ weighs $12 \ g$ and contains atoms $X$ and $Y$ in the ratio of $2:5$. The percentage of metal $X$ in the alloy is $20$ by mass. If the atomic mass of $X$ is $40$,what is the atomic mass of metal $Y$ (in $amu$)?

Isotope	Relative abundance $(\%)$	Atomic mass $(u)$
$^{12}C$	$98.8$	$12$
$^{13}C$	$1.18$	$13.1$
$^{14}C$	$0.02$	$14.1$

From the above data,what is the average molecular mass of $CH_4$ containing all isotopes of carbon,assuming hydrogen is only $^{1}_{1}H$? (Given that atomic mass of hydrogen $= 1.008 \ u$)

The oxide of a metal has the molecular formula $M_2O_3$. If the equivalent mass of the metal is $9$,what is the molecular mass of the oxide?

Write the formulae for the following compounds:
$(a)$ Mercury $(II)$ chloride
$(b)$ Nickel $(II)$ sulphate
$(c)$ Tin $(IV)$ oxide
$(d)$ Thallium $(I)$ sulphate
$(e)$ Iron $(III)$ sulphate
$(f)$ Chromium $(III)$ oxide