What is the percentage of $H_{2}SO_{4}$ in concentrated $H_{2}SO_{4}$ (in $\%$)?

Why is iron galvanised with zinc? Can it be galvanised with copper? If not,why?

What is formed when sulfur trioxide gas is absorbed in concentrated sulfuric acid?

What happens when:
$(i)$ $A$ piece of calcium is dropped in water.
$(ii)$ Sodium is kept exposed in air.
$(iii)$ Iron nail is dipped in copper sulphate solution.
$(iv)$ Potassium is dropped in cold water.
$(v)$ Carbon dioxide is compressed in water at high pressure.
Give chemical equations involved in all the above reactions and balance them.

Which of the following methods is suitable for preventing an iron frying pan from rusting?

What is the percentage of $H_{2}SO_{4}$ in dilute sulfuric acid (in $\%$)?