Chalk powder, which primarily consists of calcium carbonate, is relatively insoluble in water. While it can react very slowly with water over time to form soluble calcium bicarbonate, the solubility of chalk powder in water is extremely low, making it effectively insoluble for most practical purposes.

Answer: A) Acid rain Explanation: Secondary pollutants include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight.   Whereas Primary pollutant are those pollutants that are directly emitted from their sources, like CO2, CO, SO2 as these gases are directly emitted form burning of fossil fuels.   Acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water, sulfuric acid etc.   Hence, Acidrain is a secondary air pollutant.

Answer: A) Physical layer Explanation: If you see that a serial interface and the protocol are both down, then you have a physical layer problem. If you see serial 1 is up, line protocol is down, then you are not receiving (Data Link) Keepalives from the remote end.

Answer: B) Coins Explanation: Numismatics is the study or collection of currency, including coins, tokens, paper money, and related objects.