Observe the oxides $CO, B_2O_3, SiO_2, CO_2, Al_2O_3, PbO_2, Tl_2O_3$. The number of acidic oxides in the list is:

Helium mixed with oxygen is used in the treatment of

Assertion : $Pb^{4+}$ compounds are stronger oxidizing agents than $Sn^{4+}$ compounds.
Reason : The higher oxidation states for the group $14$ elements are more stable for the heavier members of the group due to 'inert pair effect'.

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 $SiO_4^{4-}$.
$(D)$ $NH_4Cl + NaOH \to NH_3 \uparrow$.

Assertion : Silicones are hydrophobic in nature.
Reason : $Si-O-Si$ linkages are moisture sensitive.

The presence of $Si$ in steel gives it