Which of the following compounds is $NOT$ acidic in nature?

In the following reaction,assign the correct category for the underlined atom based on the product of complete hydrolysis at $R.T.$:
$\underline{C}O_2 + H_2O \longrightarrow H_2CO_3$

$SiCl_4$ on hydrolysis forms '$X$' and $HCl$. Compound '$X$' loses water at $1000^{\circ} C$ and gives '$Y$'. Compounds '$X$' and '$Y$' respectively are:

Ions consisting of two or more atoms which have properties similar to halide ions and contain at least one nitrogen atom are called ........

The formula of the following silicate anion structure is,where $\cdot = Si$ atom,$o = O$ atom.

Choose the acidic oxide from the following.