Mark the gas which turns lime water milky.

Nitrogen gas is absorbed by which of the following substances at high temperature to form a cyanamide derivative?

Give a brief account of the production of cement and write its properties and uses.

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T$:
$H_6\underline{Si}_2O_7 + H_2O \longrightarrow H_4SiO_4$

Rationalise the given statements and give chemical reactions:
$1$. Lead $(II)$ chloride reacts with $Cl_2$ to give $PbCl_4$.
$2$. Lead $(IV)$ chloride is highly unstable towards heat.
$3$. Lead is known not to form an iodide,$PbI_4$.

Element showing the phenomenon of allotropy is