Final answer:
If the membrane becomes permeable to Cl-, the membrane potential would likely decrease as chloride ions would enter the cell, reducing the potential difference across the membrane.
Step-by-step explanation:
If the membrane becomes permeable to Cl-, the membrane potential would likely decrease (become less negative) compared to the resting membrane potential. This occurs because the resting membrane potential in neurons is determined largely by the concentration gradients of various ions, especially K+ (potassium ions) and Na+ (sodium ions) and the differential permeability of the neuronal membrane to these ions.
When Cl- (chloride ions), which are typically in higher concentration outside of the neuron than inside, can freely move across the membrane, they will diffuse into the cell down their concentration gradient, until the point at which the electrical gradient (created by the separation of charge) balances the concentration force. The accumulation of negative charge inside the cell from the entering Cl- would counteract some of the positive charge created by the K+ ions inside the cell and the positive charge outside from Na+, thus reducing the overall potential difference across the membrane. If the membrane's permeability to Cl- increased significantly, the membrane potential could even become positive if enough chloride ions entered the cell.