Matter, Atoms and Molecules RRB PYQ

Argon is a noble gas and is monoatomic in nature, meaning it exists as individual atoms rather than forming molecules. Like other noble gases, argon is colorless, odorless, and chemically inert under most conditions, which means it does not easily react with other elements or compounds. Argon constitutes about 0.93% of the Earth's atmosphere by volume, making it the third most abundant gas in the atmosphere after nitrogen and oxygen. Its presence in the air is mainly due to the radioactive decay of potassium-40 in the Earth's crust.

When one chemical reaction causes another reaction in the same system to occur or proceed faster than it normally would, the phenomenon is properly termed an induced reaction or chemical induction. The reaction producing the effect is the inducing reaction, while the affected reaction is the induced reaction. The effect generally arises because an intermediate or product of the first reaction participates in the second reaction. Unlike a catalyst, the inducing substance may be consumed during the process. Chemical induction is commonly associated with oxidation-reduction and chain reactions.

A heterogeneous mixture is best described as a mixture whose components are visibly distinct and not uniformly distributed throughout the sample. Unlike homogeneous mixtures, the composition of a heterogeneous mixture varies from one region to another. For example, in a bowl of vegetable soup, one spoonful might have more carrots while another has more broth. These mixtures often consist of two or more phases. A classic example is oil and water, which remain separate and form two distinct liquid layers. Because the components retain their individual properties and are not chemically bonded, they can typically be separated by simple physical methods such as filtration, decantation, or even manual sorting.

The observation that sugar dissolves in water without an increase in the water level provides strong evidence that matter is made of tiny particles. This phenomenon occurs because the tiny particles of sugar separate and occupy the empty spaces between the particles of water. Since they fit into these existing gaps, the overall volume of the solution does not rise significantly. This supports the theory that matter is not continuous, meaning it is composed of millions of tiny, discrete particles that are too small to be seen individually by the naked eye. For questions regarding the nature of matter, remember that diffusion and dissolution are the two primary proofs used to show that particles are small and in constant motion.

This calculation is based on the Law of Constant Proportions, which states that a chemical compound always contains its component elements in a fixed ratio by mass, regardless of the source or total amount. In this specific case, the constant mass ratio of hydrogen to oxygen in water is 1:8, therefore, for any total mass of water, hydrogen accounts for 1/9 and oxygen accounts for 8/9 of that mass. For a 36 g sample, the amount of hydrogen is 36 x (1/9) = 4 gm and the amount of oxygen is 36 x (8/9) = 32 gm, maintaining the exact 1:8 proportion.

J.J. Thomson proposed that the atom is a uniform sphere of positive electricity in which negatively charged electrons are distributed to maintain electrical neutrality. The model is famously nicknamed the 'Plum Pudding' or 'Watermelon' model, where the red pulp represents the positive charge and the seeds represent the electrons. J.J. Thomson discovered the electron through his experiments with cathode ray tubes, for which he won the Nobel Prize in Physics in 1906. Thomson's model was eventually disproved by Ernest Rutherford's gold foil experiment, which showed that the positive charge is concentrated in a tiny central nucleus rather than spread throughout the atom. Statement 2 is incorrect because the nucleus (and hence neutrons) had not yet been discovered in Thomson's model.

Mass percentage of a solution is the mass of solute in 100 parts by mass of the solution. It is calculated as: Mass % = (Mass of solute / Mass of solution) x 100. If the initial masses of solute and solvent are x and y, then mass % = [x/(x+y)] x 100. After doubling both masses, it becomes [2x/(2x+2y)] x 100 = [x/(x+y)] x 100. Thus, doubling both solute and solvent masses does not change their mass ratio; therefore, the concentration remains the same.

The formula unit mass of CaCl2 is determined by adding the atomic mass of Ca to twice the atomic mass of Cl. The formula unit mass of an ionic compound is calculated by multiplying each atomic mass by its subscript. In CaCl2, there is one calcium atom and two chlorine atoms leading to the calculation: 40 + (2 x 35.5) = 40 + 71 = 111 u.

The large, suspended particles are capable of scattering light through Tyndall effect. Once the particles settle and are undergo sedimentation at the bottom, the scattering effect ceases. While both statements are scientifically accurate, statement 2 describes the disappearance of the effect rather than providing the underlying physical reason for why suspensions scatter light in the first place.

Dalton's Atomic Theory stated that atoms are the smallest indivisible particles of matter, but later discoveries showed that atoms contain smaller particles such as electrons, protons, and neutrons. J.J. Thomson discovered the electron in 1897 through cathode ray experiments, proving that atoms have internal structure and are not indivisible. The proton was identified by Ernest Rutherford, while the neutron was discovered by James Chadwick in 1932. The discovery of isotopes also modified Dalton's idea that all atoms of the same element have identical mass, because isotopes have the same atomic number but different mass numbers.