The total number of compounds having at least one bridging oxo group among the molecules given below is _________.

$${N_2}{O_3},{N_2}{O_5},$$ $${P_4}{O_6},{P_4}{O_7},$$ $${H_4}{P_2}{O_5},{H_5}{P_3}{O_{10}},$$ $${H_2}{S_2}{O_3},{H_2}{S_2}{O_5}$$

The correct option(s) regarding the complex

$${\left[ {Co\left( {en} \right){{\left( {N{H_3}} \right)}_3}\left( {{H_2}O} \right)} \right]^{3 + }}\,\,$$ $$\left( {en = {H_2}NC{H_2}C{H_2}N{H_2}} \right)$$ is (are)

To measure the quantity of $$MnC{l_2}$$ dissolved in an aqueous solution, it was completely converted to $$KMn{O_4}$$ using the reaction,

$$MnC{l_2} + {K_2}{S_2}{O_8} + {H_2}O \to KMn{O_4} + {H_2}S{O_4} + HCl$$ (equation not balanced).

Few drops of concentrated $$HCl$$ were added to this solution and gently warmed. Further, oxalic acid ($$225$$ $$mg$$) was added in portions till the colour of the permanganate ion disappeared. The quantity of $$MnC{l_2}$$ (in mg) present in the initial solution is ____________.

(Atomic weights in $$g\,\,mo{l^{ - 1}}:Mn = 55,Cl = 35.5$$ )

Aniline reacts with mixed acid (conc. $$HN{O_3}$$ and conc. $${H_2}S{O_4}$$) at $$288$$ $$K$$ to give P $$\left( {51\% } \right),$$ Q $$\left( {47\% } \right)$$ and R $$\left( {2\% } \right).$$ The major product(s) of the following reaction sequence is (are)