Sodium Absence
In and surrounding a neuron, if sodium(Na) was absent, the diffusion of potassium(K) would result in a disturbed resting membrane potential of more negative value because there was no sodium which is pushed in the cell so potassium leaked outside. Therefore, there was more negative inside because potassium is positively(+ve) charged so they leaked outside and there is no sodium to come inside. This is the reason for more negative resting membrane potential.