रूसी रसायनज्ञ दिमित्री इवानोविच मेंडेलीव द्वारा आवर्त सारणी तैयार करते समय ज्ञात तत्वों की संख्या कितनी थी?

The 'Drain of Wealth' theory was propounded by which Indian nationalist leader?

Which event is considered the turning point in Mahatma Gandhi's leadership in the Indian independence movement?

Which African leader is known for his non-violent opposition to colonial rule?