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Class 10 · Science · Medium
→To protect tooth enamel from decay, pH should be prevented from falling below which approximate value?
Class 10 · Science · Hard
→Phenolphthalein turns pink in an aqueous solution of sodium carbonate. What is the most appropriate reason?
Class 10 · Science · Medium
→When water is added to calcium oxide, a large amount of heat is released and calcium hydroxide is formed. What is the correct classification of this reaction?
Class 10 · Science · Hard
→An acidic solution has pH 2 and another acidic solution has pH 5. How many times higher is the hydrogen ion concentration in the first solution?
Class 10 · Science · Hard
→A solution turns red litmus blue. When ammonium chloride is added to it and heated, a pungent-smelling gas is evolved. Which gas is it?
Class 10 · Science · Hard
→When excess carbon dioxide gas is passed through sodium hydroxide solution, what can finally be the main product?
Class 10 · Science · Hard
→Dry hydrogen chloride gas is passed over dry blue litmus paper and no colour change occurs. The same gas is passed over moist blue litmus paper and it turns red. What is the reason?
Class 10 · Science · Medium
→Dilute sulphuric acid is added to zinc pieces in a test tube. The evolved gas burns with a pop sound near a burning splint. What is the correct chemical reason?
Class 10 · Science · Medium
→A farmer has highly acidic soil and wants to reduce its acidity without harming crop roots. Which substance is most suitable?
Class 10 · Science · Hard
→An unknown salt gives brown fumes on heating and leaves a yellow solid that turns white on cooling. Which salt does this indicate?
Class 10 · Science · Medium
→A student adds phenolphthalein to a colourless solution and observes a pink colour. Then dilute hydrochloric acid is added slowly and the pink colour disappears. Which conclusion is most correct?
Class 10 · Science · Medium
→A student added an acidic substance to already acidic soil. What effect is likely on plant growth?
Class 10 · Science · Medium
→Why is it not suitable to leave sodium hydroxide open in air?
Class 10 · Science · Medium
→An unknown sample reacts with acid to give a gas that turns lime water milky. Which class could the sample belong to?
Class 10 · Science · Easy
→A solution turns red litmus blue and phenolphthalein pink. Which could it be?
Class 10 · Science · Easy
→A solution turns blue litmus red but keeps phenolphthalein colourless. What is the nature of the solution?
Class 10 · Science · Easy
→If both magnesium and zinc react with dilute acid, which gas will be common in both reactions?
Class 10 · Science · Easy
→What products are generally formed in the reaction between a metal and an acid?
Class 10 · Science · Medium
→In which reaction can salt, water, and carbon dioxide all be formed?
Class 10 · Science · Medium
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