Step 1: Understanding the birth of Guru Gobind Singh.
Guru Gobind Singh, the tenth Sikh Guru, was born in Patna, Bihar, on December 22, 1666. He was the son of Guru Tegh Bahadur, the ninth Sikh Guru.
Step 2: Analyzing the options.
(A) Agra: This is incorrect as Guru Gobind Singh was not born in Agra.
(B) Mathura: This is incorrect as Guru Gobind Singh was not born in Mathura.
(C) Kashi: This is incorrect as Guru Gobind Singh was not born in Kashi.
(D) Patna: Correct. Guru Gobind Singh was born in Patna, Bihar.
Step 3: Conclusion.
The correct answer is (D) Patna, as Guru Gobind Singh was born in Patna.