Choose the pair of elements $[(\mathrm{A})$ to $(\mathrm{F})]$ which:

(i) belong to the Chalcogen family

(ii) form monovalent oxides which give alkalies in aqueous solution

(iii) form stable monovalent anions

(A) $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^1$

(B) $1 s^2 2 s^2 2 p^5$

(C) $1 s^2 2 s^2 2 p^6 3 s^1$

(D) $1 s^2 2 s^2 2 p^6 3 s^2 3 p^5$

(E) $1 s^2 2 s^2 2 p^6 3 s^2 3 p^4$

(F) $1 s^2 2 s^2 2 p^4$

Given are $$\mathrm{H}_3 \mathrm{PO}_2, \mathrm{H}_3 \mathrm{PO}_3, \mathrm{H}_3 \mathrm{PO}_4$$ and $$\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7$$. Which of the above oxacids results into two series of salts?

The order of acidic strength of boron trihalides is

Give the correct order of acidity of