A diode is reverse biased when the potential at the cathode (n-side) is higher than the potential at the anode (p-side).
(1) The potential at the anode is -12V, and the potential at the cathode is -5V. Since -12V<-5V, the diode is forward biased.
(2) The potential at the anode is 0V, and the potential at the cathode is -10V. Since 0V>-10V, the diode is forward biased.
(3) The potential at the anode is 0V, and the potential at the cathode is +5V. Since 0V<+5V, the diode is reverse biased.
(4) The potential at the anode is +5V, and the potential at the cathode is +10V. Since +5V<+10V, the diode is forward biased. Therefore, the diode in option (3) is reverse biased.
The mass of particle X is four times the mass of particle Y. The velocity of particle Y is four times the velocity of X. The ratio of de Broglie wavelengths of X and Y is: