Which stage is indicated by the given figure?

Which of the following pairs of $2,3$-butanediol are enantiomeric?

The molarity of a $0.2 \ N \ Na_2CO_3$ solution will be .......... $M$.

$A$ stick of length $L$ and mass $M$ lies on a frictionless horizontal surface on which it is free to move in any way. $A$ ball of mass $m$ moving with speed $v$ collides elastically with the stick at its end,as shown in the figure. If after the collision the ball comes to rest,then what should be the mass of the ball?

The resistance in the following circuit is increased at a particular instant. At this instant,the value of resistance is $10 \, \Omega$. The current in the circuit will be now:

Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest $pH$?