An appropriate method for molecular weight determination of chloroform $(CHCl_3)$ is:

What will be the mass of one atom of ${}^{12}C$?

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

In the standardization of $Na_2S_2O_3$ using $K_2Cr_2O_7$ by iodometry,the equivalent weight of $K_2Cr_2O_7$ is:

Vapour density of a metal chloride is $83$. If equivalent weight of the metal is $6$,its atomic weight will be . . . . . . .

Naturally occurring boron consists of two isotopes with atomic masses $10.01 \ (I)$ and $11.01 \ (II)$. The average atomic mass of natural boron is $10.81$. Find the percentage abundance of isotopes $(I)$ and $(II)$ respectively.