i. Bio-degradable pollutants :
The pollutants which can be easily decomposed by the natural biological processes are called bio-degradable pollutants.
Examples: plant wastes, animal wastes, etc.
ii. Non bio-degradable pollutants :
The pollutants which cannot be decomposed by the natural biological processes are called Non bio-degradable pollutants.
Examples : metal wastes (mainly Hg and Pb), D.D.T, plastics, nuclear wastes, etc., These pollutants are harmful to living organisms even in low concentration. As they are not degraded naturally,it is difficult to eliminate them from our environment.

When two atomic orbitals overlaps sideways, the resultant covalent bond is called a pi (\(\pi\)) bond.

This condition is not static and is dynamic, because both the forward and reverse reactions are still occurring with the same rate. No macroscopic change is observed.

The enthalpy change of a reaction either at constant volume or constant pressure is the same whether it takes place in a single or multiple steps provided the initial and final states are same.

According to Avogadro's hypothesis: V \(\alpha\) n
\(\therefore \frac{V_{1}}{n_{1}}=\frac{V_{2}}{n_{2}}=\text { constant }\)
V₁ & n₂ are the volume and number of moles of a gas and V₂ & n₂ are a different set of values of volume and number of moles of the same gas at same temperature and pressure.

One mole is the amount of substance of a system, which contains as many elementary particles as there are atoms in 12 g of carbon -12 isotope.

No the above definition is incorrect. The correct definition is Ionization energy is defined as the minimum amount of energy required to remove the most loosely bound electron from the valence shell of the isolated neutral gaseous atom in its ground state.

i) chiral molecule:
The chiral molecule is
ii) S_N2 reaction:
undergoes S_N2 reaction faster as it is a primary alkyl halide.
\( \text { (or) } \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{Cl}\\ 1 - chlorobutane\)

Benzene undergoes nitration reaction becasuse it is an elecron - rich system due to delocalised \(\pi\) electron. So it is easily attacked by electrophiles and gives substituted products.

Mechanism:
Step - I : Formafion of the electrophile:

Step - II : Formation of carbocation intermediate:
The electrophile attacks the aromatic ring to form a carbocation intermediate which is stabilised by resonance.

Step - III: Formation of nitro benzene:
The electrophile attacks the artomatic ring to fo

a) Electrophiles:
Electrophiles are reagents that are attracted towards negative charge or electron rich center. They are either positively charged ions or electron deficient neutral molecules. All Lewis acids act as electrophiles.
Neutral molecules like SnCl₄ can also act as an electrophile, as it has vacant d-orbitals which can accommodate the electrons from others.

b) Nucleophiles:
Nucleophiles are reagents that has high affinity for electro positive centers. They possess an atom has an unshared pair of electrons, and hence it is in search for an electro positive centre where it can have an opportunity to share its elections to form a covalent bond, and gets stabilised.
They are usually negatively charged ions or electron rich neutral molecules (contains one or more lone pair of electrons). AII Lewis bases act as nucleophiles.

The lattice energy of LiF is higher due to the smaller size of Li⁺ and F^-. So LiF has lower solubility.

a) HCl is a gas. It is an electron rich covalent hydride. It is a covalent molecule with strong covalent bond. However the forces between the molecules are not as strong.
b) NaH is a solid. It is an ionic hydride of group I sodium metal. It is an insoluble hydride