Matter, Atoms and Molecules RRB PYQ

The mass number (A) of an atom is defined as the sum of protons and neutrons present in its nucleus. Both protons and neutrons are located in the nucleus and are collectively referred to as nucleons. In chemical notation, the mass number is usually written as a superscript to the left of the element symbol.

In a gas, particles have kinetic energy enough to completely overcome intermolecular forces. This results in particles being far apart with large empty spaces between them, moving randomly and quickly in all directions. Gas particles are widely spaced and have no regular arrangement. In contrast, solid particles are tightly packed in a fixed lattice, and liquid particles are close together but can slide past each other. Due to high kinetic energy, gas particles move freely at high speeds and frequently collide with each other and the walls of their container.

Thomson's model, often called the 'Plum Pudding' or 'Watermelon' model, describes electrons as being embedded within a uniform positively charged sphere. The model suggests that the total negative charge of the embedded electrons is equal to the total positive charge of the sphere, making the atom as a whole electrically neutral. Unlike later models, Thomson's theory did not include a nucleus or moving electrons; instead, it envisioned them as stationary 'seeds' or 'plums' inside the 'fruit'. This was the first model proposed after the discovery of the electron by J.J. Thomson in 1897.

John Dalton gave the concept of atomic mass. He proposed that all matter is composed of tiny, indivisible particles called atoms. He was the first to suggest that every element has a unique type of atom characterized by a specific relative atomic mass. His concept of atomic mass was derived from his work on the Law of Multiple Proportions and the weights of elements that combine to form compounds. Dalton initially used the mass of a hydrogen atom as the standard for comparison, before the standard eventually shifted to Oxygen-16 and finally Carbon-12.

In a homogeneous mixture, the solute particles are extremely small, typically less than 1 nm in diameter. Because the particles are so small, they cannot be seen even with a high-power microscope, and they do not scatter a beam of light. These particles are uniformly distributed throughout the solvent and do not settle down when left undisturbed, meaning the mixture is highly stable. Due to their tiny size, solute particles in a homogeneous mixture can easily pass through filter paper, making it impossible to separate them by simple filtration.

An ozone molecule consists of three oxygen atoms and is represented chemically as O3. Ozone occurs naturally in the atmosphere. In concentrated amounts, ozone is explosive and can react with various chemical compounds. Approximately 90% of ozone is located in the stratosphere, which starts about 10-16 kilometers (6-10 miles) above Earth's surface.

In the mixture, sand settles at the bottom as it is insoluble and denser than water, while salt dissolves in water due to strong ion-dipole attractions, whereas sand is a giant covalent structure that does not interact with water molecules. This process creates a combination of a true solution and a suspension within the same beaker. Because of these different properties, the components can be separated easily by filtration, followed by evaporation to recover the salt.

According to the Bohr-Bury rules for electron distribution: Maximum electrons in the nth shell = 2n^2. The outermost shell (valence shell) cannot have more than 8 electrons. The penultimate shell cannot exceed 18 electrons; and the outermost cannot exceed 8 unless certain inner shells are filled.

Condensation is a change when a gas loses heat and changes into liquid, such as water vapour changing into water droplets. Solidification is when a liquid loses heat and changes into solid, such as water changing into ice.

Among the given statements, the correct one is 'They have strong affinity for the dispersion medium'. Lyophilic sols are solvent-loving colloids in which the dispersed particles have high affinity for the dispersion medium; they are fairly stable and not easily coagulated.