The quick answers then ...
1, Please could someone explain EPR?
EPR stands for Engine Pressure Ratio, it is a measure of the amount of thrust an engine is producing and is the pressure of the flow at the back of the engine, divided by the pressure of the flow at the front.
2, What is a "super stall" ? (don't say superman stalling?!)
A stall is when the aircraft's wings are hitting the air at to much of an angle, and the air cannot flow smoothly over the top of the wing. "Super Stall", and sometimes "Locked-in Stall" are rather out-dated terms for what is more commonly known as a "Deep stall", or when the angle of attack increases so that the disturbed air is flowing back over a "T-tail" elevator, reducing the control in pitch to the point where recovery (pitching down) is difficult or impossible.
3,How does Vmca vary with Cof G?
Vmca is defined under a set of given conditions, one of which is "the most unfavourable CofG", so the strictly correct answer here is "it doesn't vary". A rear CofG reduces the moment arm of the rudder, reducing the effectiveness in yaw, thus as the GofG moves rearward, speed must be higher to maintain control.
4,what are the adv/disadvantages of INS
Over what? Advantage - you know where you are, Disadvantage - if it breakes, you don't know where you are any more!
5,CAT how does it occur?
Different air masses, moving at different velocities, create turbulence at the boundary between the masses where they "rub up against each other".
6,what make the features of the b777 unique from other aircraft?
The B777 isn't particularly unique! It's is the world's largest twin jet, it was the first aircraft to use digital to design and electronically pre-assemble the entire airplane, first aircraft ot gain 180 min ETOPS on initial certification, the flight deck includes a Ground Maneuver Camera System, the landing gear is the largest ever incorporated into a commercial airplane etc, etc.