i am new to quad rotors i got APM 2.5.but one of my ESC is shorted can i use another  company ESC along with three previous ESC's please help me

It is not advised to use different ESCs as they might have different timings. So there is a possibility that your quad will not behave properly.
However if you have to use different ESCs then atleast make sure to calibrate them before using.

thank u

I AM INTERESTED!!

I have a question can we fit an 10" prop on a quad with an motor to motor distance of about 550mm.

YES

Thanks

nitesh no offence, but what was that question for?
motor to motor distance = 550 mm
prop size=10"
now if you have 2 motors, each with a prop on it, then you should have a little more than 10" distance between 2 motors
( 2* radius of a prop, because you have 2 halves of a prop between them.)
10" to mm = 250 mm
so there is 550-250 = 300 mm or 30 cm between props.

was that too hard?

For A micro quad is 2.5" difference from prop to prop enough or we need more.