When a mixture of two different alkyl halides reacts with metallic sodium in dry ether, the formation of a possible number of alkanes are-

Let the two different alkyl halides be $R-X$ and $R'-X$.

When this mixture reacts with metallic sodium in dry ether (Wurtz reaction), three types of coupling reactions take place.

$R-X + 2Na + X-R \rightarrow R-R + 2NaX$

$R'-X + 2Na + X-R' \rightarrow R'-R' + 2NaX$

$R-X + 2Na + X-R' \rightarrow R-R' + 2NaX$

Thus, a total of three different alkanes are formed.

Answer: Three