1. Given data

• Atomic number of nucleus: $Z = 50$
• Radius of nucleus: $R = 9 \times 10^{-13}\,\text{cm}$
• Charge of nucleus: $Q = Ze = 50 \times 1.6 \times 10^{-19}\,\text{C}$

2. Convert radius into SI unit

$1\,\text{cm} = 10^{-2}\,\text{m}$

So, $R = 9 \times 10^{-13} \times 10^{-2} = 9 \times 10^{-15}\,\text{m}$

3. Potential at the surface of a nucleus

For a spherically symmetric charged nucleus, potential at the surface is

$V = \frac{1}{4\pi\varepsilon_0}\frac{Q}{R}$

Using $\frac{1}{4\pi\varepsilon_0} = 9 \times 10^9\,\text{SI units}$

Substitute values:

$V = 9 \times 10^9 \times \frac{50 \times 1.6 \times 10^{-19}}{9 \times 10^{-15}}$

4. Simplify

First cancel $9$:

$V = 10^9 \times 50 \times 1.6 \times 10^{-4}$

because $\frac{10^{-19}}{10^{-15}} = 10^{-4}$

Now, $50 \times 1.6 = 80$

Hence, $V = 10^9 \times 80 \times 10^{-4}$

$V = 80 \times 10^5$

$V = 8 \times 10^6\,\text{V}$

5. Required integer

The question asks for:

$\underline{\hspace{1cm}} \times 10^6\,\text{V}$

So the required integer is

$8$

6. Comparison with stored answer

Stored correct answer = $8$

My derived answer = $8$

They agree.