Chemistry

Authoritative sources including Wikipedia, Britannica, and specialized materials science references confirm that tungsten has the highest melting point of all metals, approximately 3422°C. Among the given options, 4000°C (option D) is the closest to the actual melting point, which is about 3422°C. The other options (1000°C, 2000°C, 3000°C) are significantly lower and incorrect. Therefore, option D is the best choice despite being a slight overestimate.

Sodium carbonate is commonly known as washing soda, which is used in cleaning and laundry applications. The other options are incorrect: Plaster of Paris is calcium sulfate hemihydrate, and common salt is sodium chloride.

In chemistry, homologous refers to compounds in a homologous series that have the same chemical properties but differ by a repeating unit, typically a -CH2- group. Therefore, 'Same Chemical Properties' is the correct interpretation.

Water is known to have multiple crystalline phases (ice polymorphs) under different temperature and pressure conditions. As of current scientific consensus, there are 18 recognized crystalline phases of ice, making option D correct.

PVC (Polyvinyl chloride) is produced by the polymerization of vinyl chloride monomers. Propane and styrene are monomers for other polymers, and 'None of these' is incorrect.

Phosphorus, antimony, and arsenic are elements that commonly act as donor atoms in coordination chemistry due to their lone pairs of electrons. Aluminum, being a metal with empty orbitals, typically acts as an acceptor rather than a donor atom.

Graphite is considered one of the purest forms of carbon, consisting almost entirely of carbon atoms arranged in a crystalline structure. Anthracite is a type of coal containing impurities, and lampblack is a form of carbon black produced by incomplete combustion, often containing impurities as well.

Helium is the lightest noble gas in the periodic table, with an atomic number of 2 and atomic mass of about 4 u. Nitrogen, hydrogen, and oxygen are not noble gases, so they are incorrect options.

Permanent hardness in water is caused by dissolved calcium and magnesium salts that do not precipitate on boiling. Adding sodium carbonate (washing soda) precipitates these ions as insoluble carbonates, thus removing permanent hardness.

The chemical symbol for Iron is Fe, derived from its Latin name 'Ferrum'. This is a standard and universally accepted symbol in the periodic table.