निम्नलिखित में से किसे पृथ्वी पर सबसे कठोर प्राकृतिक पदार्थ के रूप में जाना जाता है?

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?