The correct answer is (d). Mughals.
Surkhi is a type of red lime mortar that was introduced in Indian architecture by the Mughals. It is a mixture of lime, sand, and red ochre, and it is used to bind bricks and stones together. Surkhi is a strong and durable material, and it has been used in many of the most famous Mughal buildings, such as the Taj Mahal.
The Kushans were an ancient Indo-Scythian people who ruled over a large empire in Central Asia and northern India from the 1st to the 3rd centuries CE. They were patrons of Buddhism and Hinduism, and they built many temples and monasteries in their empire. However, there is no evidence that they used surkhi in their architecture.
The Guptas were an Indian dynasty that ruled over much of northern India from the 4th to the 6th centuries CE. They were a golden age for Indian culture, and they made significant contributions to art, literature, and science. However, there is no evidence that they used surkhi in their architecture.
The Sultanate Sultans were a group of Muslim rulers who ruled over much of northern India from the 12th to the 16th centuries CE. They were patrons of Islamic architecture, and they built many mosques and tombs in their empire. However, there is no evidence that they used surkhi in their architecture.
The Mughals were an Indian Muslim dynasty that ruled over much of the Indian subcontinent from the 16th to the 18th centuries CE. They were patrons of art, architecture, and literature, and they built many beautiful buildings, including the Taj Mahal. Surkhi was a key material in Mughal architecture, and it was used in many of their most famous buildings.