Candela is the unit of

Match List-$I$ with List-$II$ and select the correct answer by using the codes given below the lists.

List-$I$	List-$II$
$(A)$ Distance between earth and stars	$(1)$ Microns
$(B)$ Inter-atomic distance in a solid	$(2)$ $\mathring{A}$s
$(C)$ Size of the nucleus	$(3)$ Light years
$(D)$ Wavelength of infrared laser	$(4)$ Fermi

The unit of angular acceleration in the $SI$ system is

It is estimated that per minute each $cm^2$ of the Earth receives about $2 \ cal$ $(1 \ cal = 4.18 \ J)$ of heat energy from the Sun. This is called the Solar constant. In $SI$ units,the value is: (in $W/m^2$)

What is a unit? What are fundamental units and derived units?

Universal Time $(UT)$ is based on: