what will happen if two different alkyl halides under goes wurtz reaction ?

Yes, two different alkyl halides can be used in Wurtz reaction.

Wurtz reaction is used to produce alkanes from alkyl halides.

If two different alkyl halides, say, CH3Cl and C2H5Cl are used, then three different products are formed.

C2H6 from CH3Cl, C4H10 from C2H5Cl and C3H8 from CH3Cl and C2H5Cl.

And as the mixture of 3 alkanes is formed, it is generally hard to separate the alkanes and get the alkane which is required.

Also, alkenes will also be formed to a lesser extent in Wurtz reaction.