Materials around us - class-VIII

Water is the only substance that is more dense in a liquid state than in a solid state. Liquid water is most dense when it is cold and salty. 

Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Hence do not have distinct boundaries.

Gases neither have a definite shape nor  have a definite  volume. They fill up the container completely. They are not rigid.

Solids have a definite shape and volume. For example, gold is solid and it has both shape and volume.

Liquids have lower density than solids because the particles in liquids are less tightly packed, resulting in larger intermolecular spaces compared to the rigid, closely packed structure of solids.

The term sublimation refers to a physical change of state and is not used to describe transformation of a solid to a gas in a chemical reaction. The combustion of candles, containing paraffin wax, to carbon dioxide and water vapor is not sublimation but a chemical reaction with oxygen.

The molecules of a solid are fixed within the solid, and they just vibrate about their mean position. 

Density means how much dense or rigid the particles in a matter are. 

According to ancient philosophies, the matter was classified as air, water, earth, fire, and sky. This classification is based on the sources of matter. Since there are five sources, hence it was also called as 'panch tattvas'. 

Based on the physical properties, the matter can be classified as solid, liquid, and gases.

Gallium has a very low melting point (about 29.76 degrees Celsius), meaning it can melt in the palm of a human hand, making it liquid at or near ordinary room temperature.

At STP, 1 mole of any gas occupies 22.4 liters. 2.24 liters of O2 is 0.1 moles. The molar mass of O2 is 32 g/mol. Mass = 0.1 moles * 32 g/mol = 3.2 grams. The closest option is 3.4 grams, likely due to a typo in the question or options.

The reaction is C(s) + CO2(g) -> 2CO(g). According to the stoichiometry, 1 volume of CO2 produces 2 volumes of CO. Therefore, 26cc of CO2 will produce 26 * 2 = 52cc of CO.

Though substances contract on cooling, water expand when cooled beyond ${4^0 C}$. This is known as anomalous behavior of water. The density of water is maximum at $4^0$$C$

A solid object occupies three-dimensional space, meaning it has length, breadth, and height. This distinguishes it from two-dimensional shapes (area) or one-dimensional lines.

In a physical change the chemical composition of a substance does not change. 

Solids are densely packed due to its  high intermolecular attractions so they are highly incompressible but liquid has less intermolecular attractions compared to solid.But gases have very less intermolecular attractions.So they are loosely packed.

Space occupied is given by volume which is generally measured in litres. Other units of volume include $dm^3$, gal and mL.

The molecules exert no force of attraction or repulsion upon one another. I.e., the molecules are independent of each other. This is the reason gases do not have a definite shape.

$4$ inches $=$ $0.333$ foot

Mass per unit volume can be defined as density. For example : when 1 g of water has volume of 1 mL, the density of water will be 1 g/mL.
Density $\displaystyle = \dfrac {\text {mass}}{\text {volume}}$

Volumetric flask is the most precise for measuring the volume of a liquid.

A liquid cannot be compressed because its particles are closely packed due to which it has a fixed volume.

Water vapour and steam are the gases states of matter. Gases have no definite shape and no definite volume.

Solids are held in fixed positions, they can only vibrate. Because the particles can not move, solids have a definite shape and volume, and can't flow. Because the particles are already packed closely together, solids can't easily be compressed.

A matter is something that has mass and occupies space. Both marbles and beads are matter since they have mass and occupy space. In order to measure which one occupies more space, the amount of liquid, size of the container and number of marbles and beads are required. The amount of liquid displaced by the solid will be the space occupied by the solid. Higher the displaced volume, higher the space occupied. Since space occupied is independent of mass and hence D is incorrect

Water is a liquid hence it will show all the properties of liquids, it can take the shape of container, it has fixed mass and volume and very less compressible.

The intermolecular force of attraction between the water molecules is strong enough to keep the molecules/particles bound to each other. The melting point of water is below room temperature as it is already present in the liquid state whereas, its boiling point is above room temperature, i.e; $100^oC$ and room temperature is $20^oC - 22^oC$

Intermolecular forces of attraction are maximum in solids and minimum in gases, as solids have definite shape, and particles are closely packed.

The iron table is solid because the intermolecular force of attraction of the iron table is very strong, thus it is rigid and hence cannot be deformed.