Carbon atoms stick to catalyst surface in craking processes ?
1- sintring
2- poising
3- aging
4- cocking or fouling

option D - coking or fouling

Explanation:

Coking (not cocking) is the process involving the deposition of small carbon particles (created by simply putting carbon atoms) on a catalyst's accessible surface, leading in a reduction in the area accessible for catalytic activity. This is also sometimes related to fouling catalysts or merely fouling them.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.