Which ion is essential for muscle contraction?

Which of the following molecules is linear?

An ideal gas expands in such a way that $PV^2 = \text{constant}$ throughout the process.

$A$ block of mass $2 ~kg$ is initially at rest on a horizontal frictionless surface. $A$ horizontal force $\overrightarrow{F} = (9 - x^2) \hat{i} ~N$ acts on it,starting from $x = 0$. The maximum kinetic energy of the block between $x = 0$ and $x = 3 ~m$ in joules is:

For any integer $n \geq 2$,let $I_n = \int \tan^n x \, dx$. If $I_n = \frac{1}{a} \tan^{n-1} x - b I_{n-2}$ for $n \geq 2$,then the ordered pair $(a, b)$ equals to

High purity copper metal is obtained by