In what stage do children see the world in an egocentric way?

Preoperational stage (second stage).

Explanation:  In the second stage of Child's development i.e., from the age of 2 years to 7 years approximately, which is called as Preoperational stage, a child develops a strong sense of Egocentrism. It is a situation where a child is unable to see thing from other peoples' eye and feels that everyone's reaction to something should be same as the child's. At this stage, a child is busy and completely trapped in his own dreamy world and is not ready to understand things properly.

Hence, the stage is  Preoperational stage.

d. air pressure decreases as altitude increases.

r = ρ x length / area  

ρ = r x area / length  

ρ is in ohm-meters  

in basic units, it is m³kg/s³a²  

i think this is it.