Which of the following is the correct electronic configuration of $Cr$ $(Z = 24)$?

$A$ body $A$ starts from rest with an acceleration $a_1$. After $2 \ s$,another body $B$ starts from rest with an acceleration $a_2$. If they travel equal distance in the $5^{th} \ s$ after the start of $A$,then the ratio $a_1 : a_2$ is equal to

Two particles $A$ and $B$ initially at rest move towards each other under a mutual force of attraction. At the instant when the speed of $A$ is $v$ and the speed of $B$ is $2v$,the speed of the centre of mass of the system is:

$A$ rope is used to lower a block of mass $M$ vertically by a distance $x$ with a constant downward acceleration of $\frac{g}{2}$. The work done by the rope on the block is:

Which one of the following arrangements represents the correct order of electron gain enthalpy (with negative sign) of the given atomic species :-

What are $X$ and $Y$ respectively in the following reaction?
$Z$-product $\stackrel{Y}{\longleftarrow} 2$-butyne $\stackrel{X}{\longrightarrow} E$-product