Which gas is known as 'marsh gas'? MCQ with Answer and Explanation

Explanation:
Iodine sublimes on heating, converting to vapor, leaving sand behind. Iodine vapors can be condensed. Filtration cannot separate two solids; distillation for liquids.

Explanation:
The modern periodic law, established by Henry Moseley, states that the properties of elements are periodic functions of their atomic numbers. Mendeleev’s original table was based on atomic mass, but the modern version uses atomic number which resolves anomalies like Ar (Z=18, mass 40) and K (Z=19, mass 39).

Explanation:
Urea, CO(NH₂)₂, is a straight nitrogenous fertilizer with about 46% N. It contains no phosphorus or potassium. It is converted to ammonium carbonate in soil by urease enzyme, then to nitrates.