The correct order of reactivity of hydrogen halides with ethyl alcohol is

$A$ thin liquid film formed between a $U$-shaped wire and a light slider supports a weight of $1.5 \times 10^{-2} \, N$ (see figure). The length of the slider is $30 \, cm$ and its weight is negligible. The surface tension of the liquid film is (in $, N/m$)

From the ground state electronic configuration of the elements given below,pick the one with the highest value of second ionisation energy.

If $\tan (\pi \cos \theta)=\cot (\pi \sin \theta)$,then a value of $\cos \left(\theta-\frac{\pi}{4}\right)$ among the following is

The number of unpaired electrons in a chromic ion $Cr^{3+}$ (atomic number $= 24$) is

If $a, b, c$ are in $AP$,and $b-a, c-b, a$ are in $GP$,then $a: b: c$ is