In a four cylinder petrol engine the standard firing order is: A 1-2-3-4 B 1-4-3-2 C 1-3-2-4 D 1-3-4-2

Option D is Correct

Most straight-4s, Ford Taunus V4 engine have a1-3-4-2 (D) starting sequence, however different engines layouts have different firing sequences

Volkswagen air-cooled engine 1-4-3-2

Some British Ford and Riley engines, Ford Kent engine, Riley Nine 1-2-4-3

Proton Wira VDO engine 1-2-3-4

see http://en.wikipedia.org/wiki/Firing_order

Thank you Mr. Alex and apologized for the answer because the question is not in my specialty

Out of my knowledge 

Most common: 1-3-4-2. In this order vibration is least.

My answer is "D"

The Standard firing Order is

1-3-4-2

We use Firing Order for Proper Balancing the Engine and prevent Vibration

But Now These Days Different Companies use Different Firing order depending upon his design of Engine. 

D 1-3-4-2