To find the overall percentage gain or loss, we need to calculate the net gain or loss on the two articles and then express it as a percentage of the cost price.

Let's assume the cost price of the first article is x.

Given that the shopkeeper gained 13% on the first article, the selling price of the first article will be:
Selling price = Cost price + Gain
Selling price = x + (13/100)x
Selling price = x + 0.13x
Selling price = 1.13x

Given that the shopkeeper sold the first article for 9831, we can equate the selling price to 9831:
1.13x = 9831
x = 9831/1.13
x ≈ 8700

So, the cost price of the first article is approximately 8700.

Now let's assume the cost price of the second article is y.

Given that the shopkeeper lost 13% on the second article, the selling price of the second article will be:
Selling price = Cost price - Loss
Selling price = y - (13/100)y
Selling price = y - 0.13y
Selling price = 0.87y

Given that the shopkeeper sold the second article for 9831, we can equate the selling price to 9831:
0.87y = 9831
y = 9831/0.87
y ≈ 11300

So, the cost price of the second article is approximately 11300.

Now, let's calculate the total cost price and total selling price:

Total cost price = Cost price of first article + Cost price of second article
Total cost price = 8700 + 11300
Total cost price = 20000

Total selling price = Selling price of first article + Selling price of second article
Total selling price = 9831 + 9831
Total selling price = 19662

Now, let's calculate the net gain or loss:

Net gain or loss = Total selling price - Total cost price
Net gain or loss = 19662 - 20000
Net gain or loss = -338

Since the net gain or loss is negative, it means there is an overall loss.

Now, let's calculate the overall percentage gain or loss:

Overall percentage gain or loss = (Net gain or loss / Total cost price) * 100
Overall percentage gain or loss = (-338 / 20000) * 100
Overall percentage gain or loss ≈ -1.69%

Therefore, the overall percentage gain or loss is approximately 1.69% loss, which corresponds to option C.