The below image is taken from this reference design. May I know why the two zero ohm resistors are placed there.

 

One possibility is their use as zero-ohm shunts to measure current is a Spice simulation.

 

You mean current consumed the XTAL circuit of the IC.
If yes why it is used

 

Some (but not all) crystals need a resistance in the position of R30. The lower the frequency the more likely that it is required.
I don't know of any that need a resistor in the position of R27.
My guess, is that the designer knew that the crystal sometimes needs a series resistor but couldn't remember which side it went.

 

Any occurrence such as this gives the circuit designer the option of adding components as necessary without having to hack the PCB.

 

Some (but not all) crystals need a resistance in the position of R30. The lower the frequency the more likely that it is required.

May I know why some crystals need a resistance in the position of R30?

 

May I know why some crystals need a resistance in the position of R30?

To reduce the voltage across the crystal, if needed to not overdrive the crystal.

 

May I know why some crystals need a resistance in the position of R30?

The crystal has a phase shift that is asymptotic to 180°. To make an oscillator, the phase shift has to be 180°, so, on its own, the crystal needs just that little bit extra to make it oscillate. That is provided by R30 and C18.
R30 is actually in series with the output resistance of the amplifier. For high frequency crystals, the output resistance of the amplifier in combination with C18 provides sufficient phase shift to make it oscillate.

 

The R27 may also be to reduce the drive to the crystal.

 

The R27 may also be to reduce the drive to the crystal.

May I know why.I have seen some circuits with resistor in XOUT

 

May I know why.I have seen some circuits with resistor in XOUT

R30 is in XOUT.