The molecular weight of a tribasic acid is $M$. What will be its equivalent weight?

The equivalent weight of $K_2Cr_2O_7$ in acidic medium is:

Naturally occurring boron has $20\%$ $_5B^{10}$ and $80\%$ $_5B^{11}$. The average atomic weight of boron is

$209 \ g$ of an element reacts with chlorine to form $315.5 \ g$ of its chloride. What is the weight (in $g$) of oxygen that reacts with $418 \ g$ of same element?
$(Cl = 35.5 \ u; O = 16 \ u)$

$4 \, g$ of copper is dissolved in concentrated $HNO_3$. Upon strong heating of the resulting copper nitrate solution,$5 \, g$ of its oxide is obtained. The equivalent weight of copper is ...... .

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