If the switch is closed then current will flow-

(A) From $A$ to $B$
(B) From $B$ to $A$
(C) $0$
(D) Cannot say unless resistance of galvanometer is given

Hint: The current is the movement of the electric charges in the certain direction. If the positive charge moves, it directs from the positive terminal and comes towards the negative terminal. If the electron flows, it directs away from the negative terminal and comes towards the positive terminal.

Complete answer:
From the given circuit diagram, it is clear that the circuit possesses the four resistors, battery, galvanometer and the switch. It is known that the switch is the device used to control the flow of the current in the circuit. If the switch is open, the current does not flow and if the switch is closed, then the current flows through the circuit components. In the above circuit diagram, the battery is the source of the current and the galvanometer measures the amount of the current flows. When the switch ${S_W}$ is closed, the current flows from the battery and moves to the $10\,\Omega $ resistor and from there it reaches the point $A$ . Then to the point $B$ . Hence the current flows from $A$ to $B$ .

Thus the option (A) is correct.

Note:
The galvanometer used in the above circuit, not only measures the current flow but also the direction of the current flow. When the current moves in the clockwise, the needle of the galvanometer deflects in the left and when the current moves in the anticlockwise, the needle deflects in the right side.