Current I = Charge Q / time t. The total charge of $10^7$ electrons is $Q = n \times e = 10^7 \times 1.6 \times 10^{-19} C = 1.6 \times 10^{-12} C$. Since this flow occurs in 1 second, the current is $I = 1.6 \times 10^{-12}$ A.