Circuit with one voltage source, calculating voltages at nodes
Figure 1. The reds are wrong. The greens are right.


Wrong. It should be 500 Ω, not 1 kΩ.
Wrong. It should be 500 Ω, not a short circuit.
Correct. Replace D2 with a short.
Correct. 500 Ω.
Correct. Reverse diode is open circuit.
Correct. 500 Ω is 500 Ω.



  But my question is, why is there no Voltage across the 500 ohm resistor that is on the rightmost side?


Now think! Resistor 6 is part of an open circuit. How much current is flowing through R6? From Ohm's Law what is the voltage across it? (\$ V = IR \$.)



From confused chat:



Figure 2. OP's open-circuit schematic.


  Well, there is current from -20V isn't it? Or current won't go from -20V, right? Then it's 0, but(!) AS shown here i.imgur.com/5e6TcLG.jpg, just because current is 0 doesn't mean voltage is 0....








simulate this circuit &ndash; Schematic created using CircuitLab

Figure 3. Fig. 2 redrawn keeping positive at top and negative at bottom.

Figure 3 shows the correct measurement of voltages across the circuit. Since there is an open circuit no current can flow through R1 and R2. Therefore the voltage at both ends is equal so the voltage across each resistor = 0 V. The full 20 V of the two batteries appears across the open circuit.