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

Which method is used to determine the molecular mass of a volatile substance?

The ratio of equivalent weights of $C_2H_5OH$ in the following reactions is
$(i)$ $C_2H_5OH \longrightarrow CH_3CHO$
$(ii)$ $C_2H_5OH \longrightarrow C_2H_5ONa$

Elements $X$ and $Y$ form compounds $X_2Y_3$ and $X_3Y_4$ respectively. If $0.2 \ mol$ of $X_2Y_3$ weighs $32.0 \ g$ and $0.4 \ mol$ of $X_3Y_4$ weighs $92.8 \ g$,then the atomic masses of $X$ and $Y$ are respectively:

When an ion absorbs $6 \times 10^{20}$ electrons,it gets reduced. What is the number of gram equivalents of the ion?

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.