A man bought an article for ₹800. He sold it at a profit of 15%. With that money, he bought another article and sold it at a loss of 10%. Find his overall gain/loss %.

The man bought the first article for ₹800 and sold it at a profit of 15%.

$$\text{Selling Price (SP1)} = \text{Cost Price (CP1)} \times \left(1 + \frac{\text{Profit \%}}{100}\right)$$ $$\text{SP1} = ₹800 \times \left(1 + \frac{15}{100}\right)$$ $$\text{SP1} = ₹800 \times (1 + 0.15)$$ $$\text{SP1} = ₹800 \times 1.15 = ₹920$$

With the money from the first sale (₹920), he bought another article. So, the cost price of the second article (CP2) is ₹920. He sold it at a loss of 10%.

$$\text{Selling Price (SP2)} = \text{Cost Price (CP2)} \times \left(1 - \frac{\text{Loss \%}}{100}\right)$$ $$\text{SP2} = ₹920 \times \left(1 - \frac{10}{100}\right)$$ $$\text{SP2} = ₹920 \times (1 - 0.10)$$ $$\text{SP2} = ₹920 \times 0.90 = ₹828$$

The initial cost price was ₹800, and the final selling price was ₹828.

$$\text{Overall Gain/Loss} = \text{Final Selling Price} - \text{Initial Cost Price}$$ $$\text{Overall Gain/Loss} = ₹828 - ₹800 = ₹28$$

Since the result is positive, it's an overall gain.

$$\text{Overall Gain \%} = \frac{\text{Overall Gain}}{\text{Initial Cost Price}} \times 100$$ $$\text{Overall Gain \%} = \frac{₹28}{₹800} \times 100$$ $$\text{Overall Gain \%} = \frac{28}{8} = 3.5\%$$

The calculated overall gain is 3.5%. Comparing this to the given options:
(A) 2% gain
(B) 2% loss
(C) 3% gain
(D) 3% loss

Since 3.5% gain is not an exact option, we choose the closest one. 3.5% gain is closer to 3% gain than to 2% gain.

The final answer is $\boxed{\text{C}}$