निम्नलिखित में से किस पदार्थ का व्यापक रूप से ठोस स्नेहक (solid lubricant) के रूप में उपयोग किया 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?