Matter, Atoms and Molecules RRB PYQ

When the mixture of iron (Fe) and sulfur (S) is heated, they undergo a chemical reaction to form a new substance, iron (II) sulfide (FeS). Unlike a physical mixture, the new compound (FeS) has entirely different properties from its constituents. For example, iron is magnetic, but iron sulfide is non-magnetic and cannot be separated using a magnet. A chemical change is typically irreversible by simple physical means. You cannot recover the original iron filings and sulfur powder once they have reacted to form the black, solid mass of iron sulfide. The reaction is exothermic, meaning it releases heat energy once the initial heating starts the process, often causing the mixture to glow.

Atomic radius is measured in nanometres (nm). The atomic radius is the distance from the nucleus of an atom to the outermost electron shell. It is typically on the order of 0.1 to 0.3 nanometres. This small scale is appropriate for measuring atomic dimensions, as atoms are extremely tiny.

The atomic mass of the remaining element is 14u, which corresponds to Nitrogen in the compound HNO3. The combined mass of Hydrogen and Oxygen: Mass of H atom = 1x1u = 1u; Mass of 3 O atoms = 3x16u = 48u. Subtotal = 49u. Subtract the known mass from the total molecular mass to find the mass of the remaining element (X): Total mass - known mass; X = 63u - 49u = 14u. An atomic mass of 14 corresponds to Nitrogen (N). Therefore, the compound is Nitric Acid (HNO3).

The International Union of Pure and Applied Chemistry (IUPAC) chose Carbon-12 (C-12) as the standard for measuring atomic masses. The mass of a C-12 atom is defined as exactly 12 atomic mass units (amu). This isotope contains six protons and six neutrons, providing a reliable reference point for determining the atomic masses of other elements.

Sublimation is the process where a solid changes directly into a gas without passing through the liquid state. Examples of sublimation include dry ice, which sublimates at room temperature, and solid iodine, which sublimates when heated. The opposite process, called deposition, occurs when a gas changes directly into a solid without becoming a liquid.

Among the compounds listed, H2SO4 (sulfuric acid) has the most atoms. It consists of 2 hydrogen (H) atoms, 1 sulfur (S) atom, and 4 oxygen (O) atoms, totaling 7 atoms. In comparison, CO2 has 3 atoms, Ca(OH)2 has 5 atoms, and HNO2 has 5 atoms, making sulfuric acid the compound with the highest atom count.

Solids maintain a fixed volume and shape, while liquids adapt to the shape of their container and gases expand to fill any space. This makes Statement A true. Compressibility is indeed a property of matter, but it is gases, not liquids, that display significant compressibility under high pressure. Therefore, Statement B is also true (as stated in the given context regarding gases).

The atomic mass of sodium is 23 g/mol. Given that 69 g of sodium contains 3 moles, we can calculate the atomic mass using the formula: Atomic Mass = Mass / Number of Moles = 69g / 3moles = 23 g/mol.

A selectively permeable membrane, such as a cell membrane, allows only the passage of solvent molecules (like water) while restricting solute molecules (like ions or larger particles). This selective permeability helps maintain the internal environment of the cell by controlling the movement of substances in and out.

The nucleus model of the atom was first proposed by Ernest Rutherford in 1911. Rutherford's work laid the foundation for modern atomic theory and significantly advanced the understanding of radioactivity, for which he was awarded the Nobel Prize in Chemistry in 1908. He also discovered the concept of half-life and identified different types of radiation.