Quinine,used for the treatment of malarial fever,is extracted from:

Arrange $NH_4^+$,$H_2O$,$H_3O^{+}$,$HF$,and $OH^{-}$ in increasing order of acidic nature.

Which one of the following is most effective in causing the coagulation of an $As_2S_3$ sol?

In the case of a simple pendulum executing $SHM$,at $t=0$,the bob is not at the mean position. The graph drawn between the tension $(T)$ in the string and time $(t)$ is

The number of electrons in the valence shell of the central atom of a molecule is $8$. The molecule is

The number of sigma $(\sigma)$ bonds in $but-1-ene$ is: