Graphical representation of action potential across the membrane of a neuron is shown below. The different stages of the action potential are shown with numbers 1 to 5 . Choose the correct statement about the $\mathrm{Na}^{+}$and $\mathrm{K}^{+}$ion concentration across the membrane in stage 4 .

• Correct answer
  A

  Opening of $\mathrm{K}^{+}$ion channels, leading to $\mathrm{K}^{+}$efflux.
• B

  Equilibrium is reached between $\mathrm{Na}^{+}$and $\mathrm{K}^{+}$across the membrane.
• C

  Both $\mathrm{K}^{+}$and $\mathrm{Na}^{+}$ion channels are open leading to more $\mathrm{K}^{+}$influx than that of $\mathrm{Na}^{+}$.
• D

  Opening of $\mathrm{Na}^{+}$ion channels, leading to $\mathrm{Na}^{+}$efflux.

Hence, the correct answer is option: 'A'.