Given is the following reaction: 2A + 2B ----> 2C + 2D
What expression gives the speed of the reaction?

A. v = -1/2 . d[a]/dt
B. v = d[a]/dt
C. v = -1/2 . d[c]/dt
D. v = -d[a]/dt

I am doubting between A and D so please explain why you choose a certain answer.

And what is the difference between speed of reaction and rate of reaction?

The given rxn can be simplified as A + B = C + D

Thus, option D is correct.

There''s no difference between speed adn rate. It''s the same thing.

Approve if i helped :)

A. v = -1/2 . d[a]/dt
thus, rate/speed of racn. can be expressed as;
v = -1/2d[a]/dt = -1/2 . d[b]/dt = +1/2 . d[c]/dt = = +1/2 . d[d]/dt
Out of these only one option get matched which is:
= -1/2 . d[a]/dt


Each reaction will have its own rate, depending on the catalyst.

If you choose one of the rates as a reference, and compare the other rates to it, they become relative rates.


eg 
reaction 1: 5.0 mL /min 
reaction 2: 15 mL/min --> relative rate = 3 (i.e., 3x faster than rxn 1)
reaction 3: 30 mL/min --> relative rate = 6 (i.e., 6x faster than rxn 1)

approve  plz!