Questions

Bartholomew Diaz reached the point in 1487, which the Portuguese named Cape of Good Hope (the southern most point of Africa).

I am black gold i.e charcoal. It is black when it is not used and when using it is red due to fire and when used it is in grey color as it becomes ash. 

Hierarchy is a method to structure an establishment employing various levels of administration and a vertical section, or series of command, between higher and lower levels of the organization. Superior levels dominate lower levels of the bureaucracy.

The Speaker is at the top, and the members are at the bottom.

If air contained all oxygen and no nitrogen, everything would have burnt off

Bookkeeper is the only English word that has three consecutive double letters.

Ominous is the correctly spelt word in the given options. It means that giving the worrying impression that something bad is going to happen.