The IUPAC name of the compound is:

As per the given question statement, to determine the IUPAC name of the compound CH3CHC(OCH3)CH3, we have followed the following steps:

1 . First we find the longest continuous carbon chain( parent chain). This compound contains 4 carbon parent chain. So, its root name is butane.

2 . The substituent i.e methoxy( OCH3) present on the 2nd carbon from right to left direction. So, we number the chain in that direction.

3. A double bond is present between the second and third carbon. So, we add the' -2-ene' suffix in the name.

4. Finally, we get the name of the compound as 2 - Methoxy-2-butene.

Hence, the correct option is B: i.e. 2 - Methoxy-2-butene.