Which one of the following properties of an element is not variable?

$1 \ amu$ is equal to

The atomic mass of an element is $27$. If its valency is $3$,what is the vapor density of its volatile chloride?

The equivalent weight of a divalent metal is $W$. The molecular weight of its chloride is...

$1 \ u \ (amu)$ is equal to

One gram of hydrogen is found to combine with $80 \ g$ of bromine. One gram of calcium (valency $= 2$) combines with $4 \ g$ of bromine. The equivalent weight of calcium is: