(a) What design features of the above equipment prevent it from being connected to the oxygen outlet device?
1) Colour coding (oxygen is white, suction is yellow)
2) A unique sleeve index arrangement for each wall gas
"A unique sleeve index arrangement" means "it won't fit there".
That said, people have in the past connected oxygen wall outlets to patient's joint cavities and IV lines, so there is a good reason for this unique sleeve index arrangement.
Herod, Ruth, and Rachel Markham. "Suction devices." Anaesthesia & Intensive Care Medicine 13.10 (2012): 459-462.