Which ions enter the cell at the site marked $P$ in the given diagram?

Which of these processes occur during repolarisation of nerve fibre?
$(I)$. Open $Na^+$ channel
$(II)$. Closed $Na^+$ channel
$(III)$. Closed $K^+$ channel
$(IV)$. Open $K^+$ channel

In the resting stage of a neuron,the concentration gradient is generated due to:

Which of the following statement/s is/are correct with respect to generation and conduction of nerve impulse?
i. The resting potential difference is $-70 \text{ mV}$.
ii. The voltage-gated $Na^{+}$ and $K^{+}$ channels operate together and are self-closing.
iii. At the peak of action potential,the potential difference rises to $+30$ to $+60 \text{ mV}$.
iv. In medullated nerve fibre,the action potential is conducted as a wave of membrane depolarization.
v. The resting potential is maintained by the closure of gated channels of $Na^{+}$ and $K^{+}$.

Consider the statements as True/False:
$I$. The axoplasm inside the axon contains a high concentration of $K^{+}$ and negatively charged proteins.
$II$. The axoplasm inside the axon contains a low concentration of $Na^{+}$.
$III$. The fluid outside the axon contains a low concentration of $K^{+}$.
$IV$. The fluid outside the axon contains a high concentration of $Mg^{++}$ and negatively charged proteins.
The correct option is:

The potential difference in the membrane,which is responsible for the conduction of an impulse,is brought about by a change in the membrane: