The phenomenon of physics that deals with the constitution and structure of matter at the minute scales of atoms and nuclei is

How much energy in $kWh$ is obtained by eating an ice cream labeled as $700 \ kcal$?

Estimate the average mass density of a sodium atom assuming its size to be about $2.5 \; \mathring{A}$. (Use the known values of Avogadro's number and the atomic mass of sodium). Compare it with the mass density of sodium in its crystalline phase: $970 \; kg \; m^{-3}$. Are the two densities of the same order of magnitude? If so,why?

Identify the physical parameters from the list given below that have the same dimensions:
$(i)$ Magnetic field $(B)$
$(ii)$ Energy density $(u)$
$(iii)$ Refractive index $(\mu)$
$(iv)$ Young's modulus $(Y)$
$(v)$ Dielectric constant $(K)$

The diameter of a wire measured by a screw gauge of least count $0.001 \text{ cm}$ is $0.08 \text{ cm}$. The length measured by a scale of least count $0.1 \text{ cm}$ is $150 \text{ cm}$. When a weight of $100 \text{ N}$ is applied to the wire,the extension in length is $0.5 \text{ cm}$,measured by a micrometer of least count $0.001 \text{ cm}$. The error in the measured Young's modulus is $\alpha \times 10^9 \text{ N/m}^2$. The value of $\alpha$ is . . . . . . . (Ignore the contribution of the load to Young's modulus error calculation)

Pressure exerted by a gas is found to be $50\, N/m^2$. What is the value of this pressure in the $CGS$ system?