Chemistry

Dry ice is the solid form of carbon dioxide (CO2). It sublimates at -78.5°C, turning directly from solid to gas without becoming liquid, which distinguishes it from other solids like oxygen or hydrogen.

Zirconium is essential in nuclear reactors because it has a low neutron absorption cross-section and excellent corrosion resistance, making it ideal for cladding fuel rods. The other elements listed are not commonly used for this purpose.

The drum of a photostat (photocopier) machine is typically coated with selenium because of its photoconductive properties, which allow it to hold an electrostatic charge when exposed to light, essential for the copying process.

Distillation is the process used to separate components of a solution based on differences in boiling points. In the case of a common salt (sodium chloride) solution, water can be evaporated and then condensed to recover pure water, while salt remains as residue, thus both salt and water are recovered.

Oxygen was discovered in 1774 by Joseph Priestley, who isolated it by heating mercuric oxide. This discovery is well-documented in the history of chemistry.

Salinity of seawater is typically expressed as the amount of common salt (sodium chloride) per 1 kilogram of seawater, making option A correct.

Sea water contains dissolved salts which lower its freezing point compared to fresh water sources like river or canal water. Therefore, sea water will freeze last among the options given.

The chemical name of table salt is Sodium Chloride, which is represented by the formula NaCl. This is the common salt used in cooking and food seasoning.

Diamond is an allotrope of carbon, meaning it is composed entirely of carbon atoms arranged in a crystal lattice. Therefore, the correct answer is Carbon.

Fluorine is the most electronegative element in the periodic table due to its high effective nuclear charge and small atomic radius, which strongly attracts electrons in a chemical bond.

Jabir bin Hayan is widely regarded as the founder of chemistry due to his pioneering work in alchemy and the development of experimental techniques that laid the foundation for modern chemistry.

Jabir bin Hayan is widely regarded as the founder of chemistry due to his pioneering work in alchemy and chemical processes. He introduced experimental methodology and systematic classification of substances, which laid the foundation for modern chemistry.

Jabir bin Hayan is widely recognized as the founder of chemistry due to his pioneering work in alchemy and chemical processes during the Islamic Golden Age. The other options are notable scholars but not credited with founding chemistry.

Neon gas is most commonly used in neon signs because it emits a distinct bright red-orange light when an electric current passes through it, making it ideal for colorful lighting displays.

Fluorine is the most electronegative element in the periodic table due to its high effective nuclear charge and small atomic radius, which strongly attracts electrons.

Polymerization is the chemical process of joining small molecules (monomers) to form a large molecule (polymer). This matches the description in the question, making option B correct.

Water is not optically active because it is an achiral molecule and does not rotate plane-polarized light. Sugar and tartaric acid are chiral and optically active, while sodium chlorate is also optically active due to its chiral crystal structure.

Transuranic elements are those with atomic numbers greater than 92, which is the atomic number of uranium, the last naturally occurring element in the periodic table. Elements with atomic numbers greater than 92 are synthetic and are called transuranic.

Chemistry fundamentally studies both the composition and properties of matter, as well as the changes it undergoes. Therefore, the soul of chemistry involves understanding the composition and properties of matter together.

Sodium carbonate is produced by the Solvay process, also known as the ammonia-soda process. This method uses ammonia, carbon dioxide, and brine to produce sodium carbonate efficiently.

The term 'periodicity of property' refers to the repetition of chemical and physical properties of elements at regular intervals when arranged by increasing atomic number, which is the basis of the periodic table.

Metallic substances are good conductors of electricity in both solid and liquid states because they have free electrons that can move throughout the structure in both states. Ionic substances conduct electricity only in the molten (liquid) state or when dissolved in water because their ions are free to move in these states, but they do not conduct electricity in the solid state as the ions are fixed in the lattice and cannot move. Molecular solids and covalent network solids generally do not conduct electricity in either state. Therefore, the correct answer is metallic substances.

An atom is the smallest particle of an element that can take part in a chemical reaction, making option B correct. It is not indivisible (A is outdated), and while it is a building block (C), the defining feature is its chemical reactivity. Option D is true but less precise than B.

Honey's greater viscosity is primarily due to hydrogen bonding between its sugar molecules (glucose and fructose) and water, which creates strong intermolecular attractions, increasing resistance to flow. The irregular shape of molecules or molecular size is less significant in this context.

Covalent network crystals have very strong covalent bonds extending throughout the structure, resulting in much higher melting points compared to molecular crystals, which are held together by weaker intermolecular forces.