Final answer:
Positively charged X+ ions are moved into the cell due to both chemical and electrical gradients, whereas negatively charged B- ions have a favorable chemical gradient but an opposing electrical gradient; hence, both X+ and B- ions have a net electrical force that influences their movement.
Step-by-step explanation:
The net electrical force acting on ions across a cell membrane at resting membrane potential is a result of both the chemical gradient and the electrical gradient. For positively charged ions (cations), such as X+, the electrical force will act to move them into the cell because the inside of the cell is negative relative to the outside. However, for negatively charged ions (anions), such as A- and B-, the electrical force will tend to move them out of the cell. Considering the given resting membrane potential of -70 mV, the concentration gradient for each ion must also be considered.
For ion X+ with a higher extracellular concentration (120 mM) compared to the intracellular concentration (30 mM), both the chemical and electrical gradients favor movement into the cell. Conversely, for ion A-, with equal concentrations inside and outside (100 mM), there is no net chemical gradient, but the electrical gradient would push A- out of the cell. For ion B-, with a higher extracellular concentration (140 mM) compared to intracellular (30 mM), the chemical gradient favors moving into the cell, but because B- is a negatively charged ion, the electrical gradient would resist this movement.
Therefore, X+ ions have a net electrical force acting to move into the cell, and despite B- ions having a favorable chemical gradient, the electrical gradient opposes their entry. As such, the correct option is D) both X+ and B- ions, since the motion of B- is influenced but not solely dictated by the electrical force.