Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): $\mathrm{PH}_3$ has lower boiling point than $\mathrm{NH}_3$.

Reason (R) : In liquid state $\mathrm{NH}_3$ molecules are associated through vander Waal's forces, but $\mathrm{PH}_3$ molecules are associated through hydrogen bonding.

In the light of the above statements, choose the most appropriate answer from the options given below :

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : Haloalkanes react with KCN to form alkyl cyanides as a main product while with $\mathrm{AgCN}$ form isocyanide as the main product.

Reason (R) : $\mathrm{KCN}$ and $\mathrm{AgCN}$ both are highly ionic compounds.

In the light of the above statements, choose the most appropriate answer from the options given below :

If one strand of a DNA has the sequence ATGCTTCA, sequence of the bases in complementary strand is :

In acidic medium, $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ shows oxidising action as represented in the half reaction:

$$ \mathrm{Cr}_2 \mathrm{O}_7{ }^{2-}+\mathrm{XH}^{+}+\mathrm{Ye}^{\ominus} \rightarrow 2 \mathrm{~A}+\mathrm{ZH}_2 \mathrm{O} $$

$\mathrm{X}, \mathrm{Y}, \mathrm{Z}$ and $\mathrm{A}$ are respectively are :