Given below are two statements: one is labelled as Assertion $\mathbf{A}$ and the other is labelled as Reason $\mathbf{R}$

Assertion A : Physical properties of isotopes of hydrogen are different.

Reason R : Mass difference between isotopes of hydrogen is very large.

In the light of the above statements, choose the correct answer from the options given below:

<ul> <li><strong>Assertion A:</strong> The physical properties of isotopes of hydrogen are different.</li> </ul> <p>This is true because the different isotopes of hydrogen have different masses. The mass of an atom determines its physical properties, such as its melting point, boiling point, and density.</p> <ul> <li><strong>Reason R:</strong> The mass difference between isotopes of hydrogen is very large.</li> </ul> <p>This is also true. The three isotopes of hydrogen are protium (1H), deuterium (2H), and tritium (3H). Protium has a mass of 1, deuterium has a mass of 2, and tritium has a mass of 3. The difference in mass between these isotopes is relatively large, which is why they have different physical properties.</p> <p>The reason is the correct explanation of the assertion because it explains why the physical properties of the isotopes of hydrogen are different. The different masses of the isotopes cause them to have different physical properties.</p>