In a gas$-$liquid shell and tube heat exchanger, the

Presence of a non$-$condensable gas decreases the condensing film co$-$efficient

Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature

Gases to be heated$/$cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes

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