कठोर जल में, साबुन निम्नलिखित में से किस आयन (जो कठोर जल में अपेक्षाकृत अधिक मात्रा में होते हैं) के साथ अभिक्रिया करके 'साबुन का मैल' (soap scum) बनाता है?

Which allotrope of Carbon is commonly used as a 'solid lubricant'?

Which of the following is considered the purest form of carbon among coal products?

Given below are two statements: Statement I: Denatured alcohol contains small quantity of methanol, a poisonous substance. Statement II: Methanol is poisonous because it gets oxidized to methanoic acid in liver, which coagulates the protoplasm. In the light of the above statements, choose the correct answer from the options given below: