Which group of organisms was the first to exist on Earth among the given options?

Which of the following is an oilseed crop?

At $25^{\circ} C$, the concentration of $H ^{+}$ions in $1.00 \times 10^{-3} M$ aqueous solution of a weak monobasic acid having acid dissociation constant $\left(K_a\right)=4.00 \times 10^{-11}$ is $X \times 10^{-7} M$. The value of $X$ is $...$ .
Use: Ionic product of water $\left(K_w\right)=1.00 \times 10^{-14}$ at $25^{\circ} C$

Which of the following compound$(s)$ has '$Z$' configuration?

The reagent used for converting acetylene to oxalic acid is

The mean of four observations is $3$. If the sum of the squares of these observations is $48$,then their standard deviation is