This question checks understanding of one of the most basic facts in atomic physics: the nature of the electron's charge. The electron is a fundamental subatomic particle, and its electric charge is one of nature's fixed constants, known as the elementary charge (denoted e):

e = −1.602 × 10⁻¹⁹ coulombs

This value has been measured to extraordinarily high precision (famously via Millikan's oil-drop experiment) and is found to be the same for every electron in the universe, under every condition. Some key features of this constancy are worth noting:

• The magnitude and sign of the charge never change — an electron is always negatively charged; it does not flip to positive charge under any environmental, thermal, or chemical condition.
• The charge is independent of the electron's speed. Even when electrons travel at relativistic speeds (a significant fraction of the speed of light), their charge stays exactly e; only their relativistic mass and momentum change with speed, not their charge.
• The charge does not depend on the surrounding magnetic or electric field. External fields can exert a force on the electron and alter its trajectory (this is precisely how cathode ray tubes and mass spectrometers work), but they do not alter the intrinsic charge value itself.
• The electron's charge is the smallest known unit of free electric charge in nature, and the charge of any macroscopic object is always an integer multiple of this elementary charge — a principle known as charge quantization.

Given this, the correct description is that the electron carries a constant negative charge, independent of external physical conditions. The other options are incorrect because they falsely suggest the charge could become positive, could vary with the electron's speed or energy, or could depend on an external magnetic field — none of which happens; only quantities like relativistic mass or momentum are affected by speed, while charge itself remains an invariant property of the particle.