237) The green layer formed on Cu in atmosphere is due to the formation of:

238) In Lassaigne′test, if Fe³⁺ ions are in excess, the blue colour of ferriferrocyanide appears:

239) Which of the following gases is coloured:

240) When CO₂ is passed into lime water, it turns milky. When excess of CO₂ is passed, milkiness disappears because:

241) Black ppt. A dissolves in HNO₃ giving B, which gives white ppt. C with NH₄OH. C on reaction with HCl gives solution D, which gives white turbidity on addition of water. What is D?