When potassium iodide is added to an aqueous solution of potassium ferricyanide, a reversible reaction is observed in which a complex $\mathbf{P}$ is formed. In a strong acidic medium, the equilibrium shifts completely towards $\mathbf{P}$. Addition of zinc chloride to $\mathbf{P}$ in a slightly acidic medium results in a sparingly soluble complex Q.

The number of zinc ions present in the molecular formula of $\mathbf{Q}$ is _______.

Considering only the principal values of the inverse trigonometric functions, the value of

$$ \tan \left(\sin ^{-1}\left(\frac{3}{5}\right)-2 \cos ^{-1}\left(\frac{2}{\sqrt{5}}\right)\right) $$

is

Let $S=\left\{(x, y) \in \mathbb{R} \times \mathbb{R}: x \geq 0, y \geq 0, y^2 \leq 4 x, y^2 \leq 12-2 x\right.$ and $\left.3 y+\sqrt{8} x \leq 5 \sqrt{8}\right\}$. If the area of the region $S$ is $\alpha \sqrt{2}$, then $\alpha$ is equal to

Let $k \in \mathbb{R}$. If $\lim \limits_{x \rightarrow 0+}(\sin (\sin k x)+\cos x+x)^{\frac{2}{x}}=e^6$, then the value of $k$ is