Nisha buys products priced at Rs. 5, Rs. 2, and Rs. 1 in quantities \(a\), \(b\), and \(c\) respectively, with the total cost being Rs. 20:
\[5a + 2b + 1c = 20\]
She receives 3 additional Rs. 1 products because the shopkeeper had no change:
\[c_{\text{new}} = c + 3\]
Total number of products Nisha has:
\[a + b + c_{\text{new}} = a + b + c + 3\]
Given valid \(a\), \(b\), and \(c\) that solve the equation, one such solution is \(a = 2\), \(b = 3\), and \(c = 4\):
\[2 + 3 + (4 + 3) = 2 + 3 + 7 = 12\]
Thus, the number of products with Nisha at the end is:
Answer: D (10)