How many moles are there in $4.9 \ g$ of $H_{2}SO_{4}$?

Give reasons for the following:
$(i)$ Moist air and acidic gases are not good for some metals.
$(ii)$ Chips manufacturers usually flush bags of chips with nitrogen gas.

Balance the following chemical equations and identify the type of chemical reaction.
$(a)$ $Mg(s) + Cl_2(g) \to MgCl_2(s)$
$(b)$ $HgO(s) \xrightarrow{\text{Heat}} Hg(l) + O_2(g)$
$(c)$ $Na(s) + S(s) \xrightarrow{\text{Fuse}} Na_2S(s)$

Write a balanced chemical equation for each of the following reactions and also classify them.
$(a)$ Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
$(b)$ $A$ piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

The following diagram displays a chemical reaction. Observe it carefully and answer the following questions:
$(a)$ Identify the type of chemical reaction that will take place and define it. How will the colour of the salt change?
$(b)$ Write the chemical equation of the reaction that takes place.
$(c)$ Mention one commercial use of this salt.

Observe the given figure and answer the following questions:
$(i)$ Write the complete balanced chemical equation for the reaction.
$(ii)$ Write the type of reaction involved.
$(iii)$ Is there any precipitate formed?
$(iv)$ If any precipitate is formed,write the colour of the precipitate.