The dew point temperature lines on psychrometric charts are straight inclined sloping downwards to the right. When relative humidity of moist air is $100\%,$ then

Wet bulb temperature$=$dry bulb temperature

Wet bulb temperature$=$dew point temperature

Saturation temperature$=$dew point temperature

All $\text{'}$a$\text{'},\text{'}$b$\text{'}$ & $\text{'}$c$\text{'}$