Chemistry

1.26 Quartzis crystalline solid with long range order and glass is amorphous solid (or pseudo solid or super cooled liquid) with short range order and has a tendency to flow. When quartzis heated, it can be converted into glass.

1.25 Amorphous solids have short-range order with irregular shapes of constituent particles. They have isotropic nature and melt over a range of temperatures. They do not have a definite enthalpy of fusion. Examples of amorphous solids are glass, rubber, plastic, etc.

3.28. The elements of Group I have only one electron in their respective valence shells and thus have a strong tendency to lose this electron. The tendency to lose electrons in turn, depends upon the ionization enthalpy. Since the ionization enthalpy decreases down the group therefore, the reactivity of group 1 elements increases in the order Li < Na < K < Rb < Cs. In contrast, the elements of group 17 have seven electrons in their respective valence shells and thus have strong tendency to accept one more electron to make stable configuration. So for group 17, the electron gain enthalpy and electronegativity decreases down the group and thus the reactivity also decreases.

Mechanism of formation of photochemical smog:

3.27.  (a) Element belonging to nitrogen family (group 15) e.g., nitrogen.

(b) Element belonging to alkaline earth family (group 2) e.g., magnesium.

(c) Element belonging to oxygen family (group 16) e.g., oxygen.

The word smog is a combination of smoke and fog. It is a type of air pollution that occurs in many cities throughout the world. Classical smog occurs in a cool, humid climate. It is also called reducing smog. Whereas photochemical smog (photo means light) occurs in warm and dry sunny climates. It has a high concentration of oxidising agents and therefore, it is also called oxidising smog.

1.24 Ferromagnetic substances would make better permanent magnets because when the ferromagnetic substance is placed in a magnetic field, all domains get oriented in the direction of magnetic field and strong a magnetic effect is produced.

This is mainly due to the large number of industries and power plants in the nearby areas. Acid rain has vapours of sulphuric acid dissolved in it. When it comes in contact with various statues or monuments, the acid reacts chemically with marble (calcium carbonate).
CaCO₃ + H₂SO₄ à CaSO₄ + H₂O + CO₂

As a result, the monument is being slowly disfigured, and the marble is getting discoloured and lustreless.

3.26.