The straight lines represented by the equation $9x^2 - 12xy + 4y^2 = 0$ are

$A$ Carnot engine whose low temperature reservoir is at $7^{\circ} C$ has an efficiency of $50 \%$. It is desired to increase the efficiency to $70 \%$. By how many degrees should the temperature of the high temperature reservoir be increased? (in $K$)

$A$ molecule $(X)$ has $(i)$ four sigma bonds formed by the overlap of $sp^2$ and $s$ orbitals,$(ii)$ one sigma bond formed by $sp^2$ and $sp^2$ orbitals,and $(iii)$ one $\pi$ bond formed by $p_z$ and $p_z$ orbitals. Which of the following is $X$?

When a body moves with a constant speed along a circle,

Which one of the following precedes the re-formation of the nuclear envelope during the $M$ phase of the cell cycle?

Maximum bond angle is present in