Which property of $CO_2$ makes it biologically and geo-chemically important?

What is the increasing order of stability of the $+2$ oxidation state for the given group $14$ elements?

Explain the following reactions:
$(a)$ Silicon is heated with methyl chloride at high temperature in the presence of copper;
$(b)$ Silicon dioxide is treated with hydrogen fluoride;
$(c)$ $CO$ is heated with $ZnO$;
$(d)$ Hydrated alumina is treated with aqueous $NaOH$ solution.

Give the preparation of carbon monoxide. Explain the properties of carbon monoxide and give its uses.

Give reasons for the following:
$(i)$ $CCl_4$ is immiscible in water,whereas $SiCl_4$ is easily hydrolyzed.
$(ii)$ Carbon has a strong tendency for catenation compared to silicon.

Mark the gas which turns lime water milky.