Qandahar was lost to the __________ during the reign of Shah Jahan.​

Correct option is D

Qandahar was lost to the Safavids during the reign of Shah Jahan: 

• Capture by Shah Jahan: In 1638, Shah Jahan and his sons captured Kandahar from the Safavids. However, the Safavids recaptured the city in 1649. 
• Mughal attempts to retake Kandahar: The Mughals attempted to retake Kandahar during the Mughal–Safavid war of 1649–1653, but their efforts were unsuccessful. The Mughals laid siege to the city three times, but all three sieges failed. 
• Shah Jahan's decision to stop attempts: By 1653, Shah Jahan stopped all attempts to retake Kandahar. 

The loss of Kandahar was a significant blow to the Mughal Empire.