The combined gas law is represented by: MCQ with Answer and Explanation

Explanation:
Pure water consists only of H₂O molecules, which barely dissociate into H⁺ and OH⁻ ions (10⁻⁷ M). Due to the extreme lack of free ions, it is a very poor conductor. Adding acids, bases, or salts provides ions, making it a good conductor. Both statements are correct and R explains A.

Explanation:
Hydration of cement is exothermic (heat of hydration). In large concrete pours, this heat can cause thermal cracking. Cooling is sometimes needed.

Explanation:
Oxygen (O₂) is an element, a pure substance. Milk is a colloid; brass is an alloy (mixture); sea water is a solution (mixture). Pure substances have fixed composition.