Units and Measurement

Angstrom, Micron and light year are all units of length but radian is the unit of angle subtended.

The parsec is a unit of length used to measure the large distances to astronomical objects outside the Solar System. One parsec is approximately equal to 31 trillion kilometres or about 3.26 light-years. One parsec is the distance to an object whose parallax angle is one arcsecond.

Pound is a unit of mass in the F.P.S. system.

Foot is the unit of length in the F.P.S. system.

Tonne is a non-metric system defined unit of mass.
$1 \ tonne = 1000 \ kg$

$1$ Light year $=9.461\times 10^{15}\,m$

The basic metric unit of mass is kilogram

Kilogram is the basic unit of mass in the metric system

Specific heat- $J/kg^oC$
Latent Heat- J/kg
Electrical potential difference- J/coulumb
Electrical resistance- ohm
 Hence, option C and D are correct

Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter $(S/m)$

Metre is the SI unit of length.
$1 \ millimetre = 10^{-3} \ metre$
$1 \ angstrom = 10^{-10} \ metre$
$1 \ fermi = 10^{-15} \ metre$
So, fermi is the smallest unit.