This question is based on Heisenberg's Uncertainty principle, which states that the position and the velocity of a subatomic particle like an electron cannot be measured with absolute certainty.

Since the mass of the electron is a fixed quantity, the change in the momentum is actually the change in the velocity of the electron.

The pair of position and momentum in the Heisenberg’s Uncertainty principle are called complementary variables.The measurement of the position of an electron is done with the help of an electron microscope and the accuracy of such measurement is limited by the wavelength of the light illuminating the electron.