The correct order of the dynasties of the Delhi Sultanate in chronological order is option 4: d, a, b, c.

To better understand each option:

Option 1: This option suggests the order as Slave (d), Khilji (a), Sayyad (c), and Tughlaq (b). This is incorrect as it does not follow the chronological order.

Option 2: This option suggests the order as Khilji (a), Slave (d), Tughlaq (b), and Sayyad (c). This is incorrect as it also does not follow the chronological order.

Option 3: This option suggests the order as Khilji (a), Tughlaq (b), Sayyad (c), and Slave (d). This is incorrect as it does not follow the chronological order.

Option 4: This option suggests the correct order as Slave (d), Khilji (a), Tughlaq (b), and Sayyad (c). This follows the chronological order as the Slave dynasty came first, followed by the Khilji dynasty, then the Tughlaq dynasty, and finally the Sayyad dynasty.