For alkali metals, which one of the following trends is incorrect?

Fill in the blanks:
$(1)$ Sodium hydroxide is also known as ......
$(2)$ The reaction of sodium amalgam with water produces ...... and ...... gas.
$(3)$ Sodium hydroxide on reaction with $CO_2$ produces ......
$(4)$ Sodium hydrogen carbonate is known as ......

$CO_2 + NH_3 + H_2O \to X$
$X + NaCl \to Y + NH_4Cl$
$2Y \xrightarrow{\Delta} Z + H_2O + CO_2$. '$Z$' is

$2Na_2O \overset{400 \ ^oC}{\rightleftharpoons} A + 2Na$
$A + SO_2 \to Na_2SO_4$
$A + CO \to Na_2CO_3$
In the above reaction,$A$ is:

What is the chemical formula of Indian saltpeter?

Alkali metals possess metallic lustre when freshly cut because