To solve this problem, we need to understand the concept of loss and gain percentages.

Given information:
- Loss percentage: 9%
- Rate of selling: 15 pencils for 1 rupee

To find the number of pencils we must sell for a rupee to gain 5%, we can follow the steps below:

1. Calculate the cost price of one pencil:
Since we are selling 15 pencils for 1 rupee, the cost price of one pencil can be calculated by dividing the selling price by the number of pencils:
Cost price of one pencil = 1 rupee / 15 pencils = 1/15 rupee

2. Calculate the selling price after a loss of 9%:
To calculate the selling price after a loss of 9%, we subtract the loss percentage from 100% and multiply it by the cost price:
Selling price after a loss of 9% = (100% - 9%) * (1/15 rupee) = 91% * (1/15 rupee)

3. Calculate the selling price after a gain of 5%:
To calculate the selling price after a gain of 5%, we add the gain percentage to 100% and multiply it by the cost price:
Selling price after a gain of 5% = (100% + 5%) * (1/15 rupee) = 105% * (1/15 rupee)

4. Calculate the number of pencils for 1 rupee to gain 5%:
To find the number of pencils we must sell for a rupee to gain 5%, we divide 1 rupee by the selling price after a gain of 5%:
Number of pencils for 1 rupee to gain 5% = 1 rupee / (105% * (1/15 rupee))

Simplifying the expression:
Number of pencils for 1 rupee to gain 5% = 1 / (105/100 * (1/15)) = 1 / (105/100 * 15/1) = 1 / (7/20) = 20/7 = 2.857

Since we cannot sell a fraction of a pencil, we need to round up the result:
Number of pencils for 1 rupee to gain 5% = 3 pencils

Therefore, the correct answer is option B) 13 pencils.