Which of the following figure represents forward bias diode?

A diode is forward-biased if the anode potential exceeds the cathode potential: $V_{\text{anode}} > V_{\text{cathode}}$.

For option (A): $V_{\text{anode}} = 0\, \text{V}$, $V_{\text{cathode}} = -4\, \text{V}$, so $0 > -4$ and $0\, \text{V} - (-4\, \text{V}) = +4\, \text{V}$. The diode is forward-biased.

For option (B): $V_{\text{anode}} = -4\, \text{V}$, $V_{\text{cathode}} = -3\, \text{V}$, so $-4 < -3$ and $-4\, \text{V} - (-3\, \text{V}) = -1\, \text{V}$. The diode is reverse-biased.

For option (C): $V_{\text{anode}} = -2\, \text{V}$, $V_{\text{cathode}} = +2\, \text{V}$, so $-2 < 2$ and $-2\, \text{V} - 2\, \text{V} = -4\, \text{V}$. The diode is reverse-biased.

For option (D): $V_{\text{anode}} = +3\, \text{V}$, $V_{\text{cathode}} = +5\, \text{V}$, so $3 < 5$ and $3\, \text{V} - 5\, \text{V} = -2\, \text{V}$. The diode is reverse-biased.

The only forward-biased diode corresponds to option (A).