Detailed Explanation:

Lala Lajpat Rai was the first Indian leader to use the Safety-Valve Theory to criticize the Moderates in the Indian National Congress.

The theory, proposed by W.C. Bonnerjee and A.O. Hume, suggested that the Congress was created by the British to act as a safety valve to release anti-British sentiments peacefully and prevent another 1857-like uprising.

Lala Lajpat Rai used this theory in his criticism to argue that the Moderates were serving British interests rather than genuinely fighting for Indian independence.