$M{L^{ - 1}}{T^{ - 2}}$ represents:

Give an example of:
$(a)$ a physical quantity which has a unit but no dimensions
$(b)$ a physical quantity which has neither unit nor dimensions
$(c)$ a constant which has a unit
$(d)$ a constant which has no unit

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$(a)$ ${R}_{H}$ (Rydberg constant)	$(i)$ ${kg} {m}^{-1} {s}^{-1}$
$(b)$ $h$ (Planck's constant)	$(ii)$ ${kg} {m}^{2} {s}^{-1}$
$(c)$ $u_{B}$ (Magnetic field energy density)	$(iii)$ ${m}^{-1}$
$(d)$ $\eta$ (Coefficient of viscosity)	$(iv)$ ${kg} {m}^{-1} {s}^{-2}$

Choose the most appropriate answer from the options given below:

In an electromagnetic system,a quantity defined as the ratio of electric dipole moment and magnetic dipole moment has dimensions of $[M^P L^Q T^R A^S]$. The values of $P$ and $Q$ are:

State,for each of the following physical quantities,if it is a scalar or a vector: volume,mass,speed,acceleration,density,number of moles,velocity,angular frequency,displacement,angular velocity.

State whether the following statements are true or false:
$(a)$ $A$ physical quantity can have units but still be dimensionless.
$(b)$ Impulse and the gradient of energy have the same units.
$(c)$ The absolute error in every measurement is equal to the least count of the measuring instrument.