For the following reaction, the equilibrium constant K_c at 298 K is 1.6 $$ \times $$ 10¹⁷.

Fe²⁺(aq) + S^2-(aq) ⇌ FeS(s)

When equal volumes of

0.06 M Fe²⁺(aq) and 0.2 M S^{2$$ - $$}(aq)

solutions are mixed, the equilibrium concentration of Fe²⁺(aq) is found by Y $$ \times $$ 10^{$$ - $$17} M. The value of Y is .................

At 143 K, the reaction of XeF₄ with O₂F₂ produces a xenon compound Y. The total number of lone pair(s) of electrons present on the whole molecule of Y is .................

Schemes 1 and 2 describe the conversion of P to Q and R to S, respectively. Scheme 3 describes the synthesis of T from Q and S. The total number of Br atoms in a molecule of T is .................

Let S be the set of all complex numbers z satisfying $$\left| {z - 2 + i} \right| \ge \sqrt 5 $$. If the complex number z₀ is such that $${1 \over {\left| {{z_0} - 1} \right|}}$$ is the maximum of the set $$\left\{ {{1 \over {\left| {{z_0} - 1} \right|}}:z \in S} \right\}$$, then the principal argument of $${{4 - {z_0} - {{\overline z }_0}} \over {{z_0} - {{\overline z }_0} + 2i}}$$ is