Identify the relevant compounds

• Maleic acid = cis-but-2-enedioic acid
• Fumaric acid = trans-but-2-enedioic acid
• Maleic anhydride is the cyclic anhydride formed from maleic acid.

Recall how cyclic anhydrides are formed

Dicarboxylic acids form cyclic anhydrides on heating only when the two $-COOH$ groups can come close enough to eliminate water intramolecularly.

This is possible for the cis isomer, but not for the trans isomer.

Check each option

A: Heating trans-but-2-enedioic acid

• Trans-but-2-enedioic acid is fumaric acid.
• In the trans form, the two $-COOH$ groups are on opposite sides, so cyclic anhydride formation is not favored.
• Incorrect.

B: Heating cis-but-2-enedioic acid

• Cis-but-2-enedioic acid is maleic acid.
• On heating, it undergoes intramolecular dehydration to form maleic anhydride.
• Correct.

The reaction is: $\text{Maleic acid} \xrightarrow{\Delta} \text{Maleic anhydride} + H_2O$

C: Treating cis-but-2-enedioic acid with alcohol and acid

• Alcohol + acid generally gives esterification, not anhydride formation.
• Incorrect.

D: Treating trans-but-2-enedioic acid with alcohol and acid

• This also leads toward ester formation, not maleic anhydride.
• Incorrect.

Conclusion

Maleic anhydride is prepared by heating cis-but-2-enedioic acid.

Therefore, the correct option is: $\boxed{\text{B}}$