In a compound such as water,the ratio of the mass of hydrogen to the mass of oxygen is always

Calculate the number of moles of magnesium present in a magnesium ribbon weighing $12 \, g$. The molar atomic mass of magnesium is $24 \, g \, mol^{-1}$. (in $, mol$)

State the postulate of Dalton's atomic theory which led to the law of conservation of mass. Calculate the molecular mass of water.

Nitrogen and hydrogen combine in the ratio $14:3$ by mass to form an ammonia molecule. Find the formula of the ammonia molecule by calculating the molar ratio. (Given atomic mass of $N = 14 \ u, H = 1 \ u$)

Classify each of the following on the basis of their atomicity:
$(a) F_2$
$(b) NO_2$
$(c) N_2O$
$(d) C_2H_6$
$(e) P_4$
$(f) H_2O_2$
$(g) P_4O_{10}$
$(h) O_3$
$(i) HCl$
$(j) CH_4$
$(k) He$
$(l) Ag$

Which amongst the following has a greater number of atoms,$11.5 \, g$ of sodium $(Na)$ or $15 \, g$ of calcium $(Ca)$? How? (Given: atomic mass of $Na = 23 \, u$,$Ca = 40 \, u$)