1. Analyze Statement 1

   Statement 1 says: For practical purposes, the earth is used as a reference at zero potential in electrical circuits.

   This is True.

   • The earth is a very large conductor.
   • Because of its enormous size, it can accept or supply charge without appreciable change in its potential.
   • Hence, in practice, it is taken as the reference point of zero potential.

2. Analyze Statement 2

   Statement 2 says: The electrical potential of a sphere of radius $R$ with charge $Q$ uniformly distributed on the surface is given by $V=\frac{Q}{4\pi \varepsilon_0 R}$

   This is also True.

   For a charged spherical shell (or conducting sphere), the potential at the surface is $V=\frac{1}{4\pi\varepsilon_0}\frac{Q}{R}$

   So Statement 2 is correct.

3. Check whether Statement 2 explains Statement 1

   Statement 1 is about why the earth can be taken as zero potential reference.

   The relevant idea is that for a spherical conductor, $V=\frac{1}{4\pi\varepsilon_0}\frac{Q}{R}$ and since the earth has a very large radius $R$, even if it gains or loses some charge, its potential changes only negligibly.

   However, Statement 2 merely gives the formula for the potential of a charged sphere. By itself, it does not explicitly explain the practical grounding idea unless we additionally apply it to the earth’s enormous radius.

   In assertion-reason type questions, the explanation must directly justify Statement 1. Here Statement 2 is true, but it is not the correct explanation as stated.

4. Evaluate the options

   • A: Both true, and 2 explains 1 → Incorrect
   • B: Both true, but 2 does not explain 1 → Correct
   • C: 1 true, 2 false → Incorrect
   • D: 1 false, 2 true → Incorrect

Final Answer

Option B is correct.