Competitive Thinking

$1.0 \mathrm{g}$ of magnesium is burnt with $0.56 \mathrm{g}$${\mathrm{O}}_2$ in a closed vessel. Which reactant is left in excess and how much?
(At. wt. $\mathrm{Mg} = 24; \mathrm{O} = 16$)

The ratio of masses of oxygen and nitrogen in a particular gaseous mixture is $1:4$. The ratio of their number of molecules is

The most abundant elements by mass in the body of a healthy human adult are:
Oxygen$(61.4 \%)$, Carbon$(22.9 \%)$, Hydrogen$(10.0 \%)$ and Nitrogen$(2.6 \%)$. The weight, which a $75 \mathrm{kg}$ person would gain if all ${}^1\mathrm{H}$ atoms are replaced by ${}^2\mathrm{H}$ atoms is,

$20.0 \mathrm{g}$ of a magnesium carbonate sample decomposes on heating to give carbon dioxide and $8.0 \mathrm{g}$ of magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (Atomic Weight: $\mathrm{Mg}=24$)

Haemoglobin contains $0.33\%$ of iron by weight. The molecular weight of haemoglobin is approximately $67,200$. The number of iron atoms (Atomic weight of $\mathrm{Fe}=56$) present in one molecule of haemoglobin is 

If the Avogadro number${\mathrm{N}}_{\mathrm{A}}$, is changed from $6.022 \times {10}^{23} {\mathrm{mol}}^{-1} \text{to} 6.022 \times {10}^{20} {\mathrm{mol}}^{–1}$ this would change

Suppose the elements $\mathrm{X}$ and $\mathrm{Y}$ combine to form two compounds ${\mathrm{XY}}_2$ and ${\mathrm{X}}_3{\mathrm{Y}}_2$. When $0.1$ moles of ${\mathrm{XY}}_2$ weighs$10 \mathrm{g}$ and $0.05$ moles of ${\mathrm{X}}_3{\mathrm{Y}}_2$ weighs $9 \mathrm{g}$, the atomic weights of $\mathrm{X}$ and $\mathrm{Y}$ are

Which symbol replaces the unit of atomic mass, amu?