Tetrahalides of group $14$ elements (except that of carbon) act as

$A$ certain element forms a solid oxide which when dissolved in water forms an acidic solution. The element is:

$(a)$ Classify the following oxides as neutral,acidic,basic,or amphoteric:
$CO, B_2O_3, SiO_2, CO_2, Al_2O_3, PbO_2, Tl_2O_3$
$(b)$ Write suitable chemical equations to show their nature.

Which of the following,on reaction with water,will have a $pH$ less than $7$?

Which one of the following is used as a refrigerant for ice-cream and frozen foods?

For correct statement use $T$ and for incorrect use $F$:
$(A)$ Hydrolysis of Marshall's acid gives $H_2SO_4$ and $H_2O_2$ as final products.
$(B)$ In $SCNSiH_3$ structure,the geometry around $N$ is bent.
$(C)$ The basic unit for silicates is $SiO_4^{4-}$.
$(D)$ $NH_4Cl + NaOH \to NH_3 \uparrow$.