Assertion- Angular momentum of a single electron in any orbit of hydrogen type atoms is independent of the atomic number of the element.

Reason- In the ground state angular momentum is minimum.

Assertion- The energy of continuous $\mathrm{X}$—rays is more than the energy of characteristic $\mathrm{X}$—rays.

Reason- Characteristic $\mathrm{X}$—rays are produced due to the transition of electrons from higher energy states to lower energy states.

Assertion- Wavelength of characteristic $\mathrm{X}$-rays are given by $\frac{1}{\lambda }\propto \left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$ in the transition from $n_2$ to $n_1$. In the above relation proportionality constant does not depend upon the target material.

Reason- Continuous $\mathrm{X}$-rays are target independent.

Assertion- Wavelength of characteristic $X$-rays is given by $\frac{1}{\lambda }\propto \left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$ in transition from $n_2$ to $n_1$. In the above relation proportionality constant is series dependent. For different series ($\mathrm{K}$-series, $\mathrm{L}$-series, etc) value of this constant will be different.

Reason- For $\mathrm{L}$-series value of this constant is less than the value for $\mathrm{K}$-series.

Assertion- If high pressure is applied to a radioactive substance, rate of radioactivity will increase.

Reason- Radioactivity is a nuclear process.

Assertion- At time $t=0$, the activity of a radioactive substance is $100 \mathrm{units}$. At $t=1 \mathrm{s}$, it remains $90 \mathrm{units}$. Then at $t=2 \mathrm{s}$, it should remain $80 \mathrm{units}$.

Reason- In the equal interval of time, percentage change is equal. 

Assertion- If light continuously falls on a metal surface, then the emission of electrons will stop after some time.

Reason- We cannot extract all the electrons of a metal.