What is the coordination number of the metal in $[Co(en)_2Cl_2]^+$?

Which among the following is a benzylic halide?

The mean and the standard deviation (s.d.) of $10$ observations are $20$ and $2$ respectively. Each of these $10$ observations is multiplied by $p$ and then reduced by $q$,where $p \neq 0$ and $q \neq 0$. If the new mean and new s.d. become half of their original values,then $q$ is equal to

The acute angle between the line $\vec{r}=(\hat{i}+2\hat{j}+\hat{k})+\lambda(\hat{i}+\hat{j}+\hat{k})$ and the plane $\vec{r} \cdot(2\hat{i}+\hat{j}+\hat{k})=5$ is

The order of the differential equation whose general solution is given by $y = (c_1 + c_2) \cos(x + c_3) - c_4 e^{x + c_5}$,where $c_1, c_2, c_3, c_4, c_5$ are arbitrary constants,is

If $S_{n} = 1^3 + 2^3 + \ldots + n^3$ and $T_{n} = 1 + 2 + \ldots + n$,then