The political conditions of Europe as follows :
(i) The first half of the nineteenth century saw an enormous increase in population all over Europe.
(ii) In most countries, there were more job seekers than employment. Population from rural areas migrated to the cities to live in overcrowded slums.
(iii) Small producers in towns were often faced with stiff competition from imports of cheap machine made goods from England, where industrialisation was more advanced than on the continent.
(iv) In these regions of Europe where the aristocracy still enjoyed power, peasants struggled under the burden of feudal dues and obligations.
(v) The rise of food prices or a year of bad harvest led to widespread pauperism in town and country.

• Political Fragmentation: Like Germany, Italy was also politically fragmented. During the middle of the 19th century, Italy was divided into seven states, of which only one, Sardinia- Piedmont was ruled by an Italian Prince.
• Role ofMazzini: Giuseppe Mazzini made efforts to unite Italian Republic. He had formed a secret society called ‘Young Italy’ for achieving his goal.
• Role of Count Cavour: He was the chief minister who led the movement to unify Italy. He formed a tactful diplomatic alliance with France and defeated the Austrian forces.
• Role of Giuseppe Garibaldi: Garibaldi also formed armed volunteers. In 1860, they marched into South Italy and the Kingdoms of Two Sicilies and succeeded in driving out the Spanish rulers.
• In 1861, Victor Emmanuel II was proclaimed King of United Italy.

Given series is 3, 8, 13, ...... 253
here, first term , a = 3
common difference , d = 5
Let us find total number of terms at first.
use {tex}\bf{T_n=a+(n-1)d}{/tex}
=> 253 = 3 + (n - 1)5
=> 250 = 5(n - 1)
=> n - 1 = 50
=> n = 51
so, there are 51 terms in given series.
now we know, mth term from last =last term - mth term + 1
so, 20th term from last = 51 - 20 + 1 = 32
hence, 20th from last = 32th term from first

use , {tex}\bf{T_{32}=a+(32-1)d}{/tex}
= 3 + 31 × 5 = 3 + 155 = 158
hence , 20th term from last = 158

Hit and Trial Method

The simplest method to balance a chemical equation is by the hit and trial method also called the trial and error method.

The method involves the following steps:
Step 1: Write the correct formulae of the reactants and the products with plus signs in between with an arrow pointing from the reactants to the products. This is called the skeleton equation.
Step 2: Select the largest formula from the skeleton equation and equalise the number of atoms of each of its constituent elements on both sides of the chemical equation by suitable multiplications.
Or
Balance the atoms of that element which occurs at the minimum number of places on both sides of the chemical equation first. Atoms which occur at a maximum number of places are balanced last of all.
Step 3: When an elementary gas (diatomic) such as hydrogen, oxygen, chlorine or nitrogen appears as a reactant or a product, the equation is balanced more easily by keeping the elementary gas in the atomic state. The balanced atomic equation is then made molecular by multiplying the whole equation by two.
Step 4: Verify that the number of atoms of each element is balanced in the final equation.
Step 5: The chemical equation can be made more informative by mentioning the physical states of the reactants and the products. Thus, the gaseous, liquid, aqueous and solid states of the reactants and products are represented by the notations (g), (l), (aq) and (s), respectively.

Hit and Trial Method

The simplest method to balance a chemical equation is by the hit and trial method also called the trial and error method.

The method involves the following steps:
Step 1: Write the correct formulae of the reactants and the products with plus signs in between with an arrow pointing from the reactants to the products. This is called the skeleton equation.
Step 2: Select the largest formula from the skeleton equation and equalise the number of atoms of each of its constituent elements on both sides of the chemical equation by suitable multiplications.
Or
Balance the atoms of that element which occurs at the minimum number of places on both sides of the chemical equation first. Atoms which occur at a maximum number of places are balanced last of all.
Step 3: When an elementary gas (diatomic) such as hydrogen, oxygen, chlorine or nitrogen appears as a reactant or a product, the equation is balanced more easily by keeping the elementary gas in the atomic state. The balanced atomic equation is then made molecular by multiplying the whole equation by two.
Step 4: Verify that the number of atoms of each element is balanced in the final equation.
Step 5: The chemical equation can be made more informative by mentioning the physical states of the reactants and the products. Thus, the gaseous, liquid, aqueous and solid states of the reactants and products are represented by the notations (g), (l), (aq) and (s), respectively.

• Sclera: It is the outer covering, a protective tough white layer called the sclera (white part of the eye).
• Cornea: The front transparent part of the sclera is called cornea. Light enters the eye through the cornea.
• Iris: A dark muscular tissue and ring-like structure behind the cornea are known as the iris. The colour of iris actually indicates the colour of the eye. The iris also helps regulate or adjust exposure by adjusting the iris.
• Pupil: A small opening in the iris is known as a pupil. Its size is controlled by the help of iris. It controls the amount of light that enters the eye.
• Lens: Behind the pupil, there is a transparent structure called a lens. By the action of ciliary muscles, it changes its shape to focus light on the retina. It becomes thinner to focus distant objects and becomes thicker to focus nearby objects.
• Retina: It is a light-sensitive layer that consists of numerous nerve cells. It converts images formed by the lens into electrical impulses. These electrical impulses are then transmitted to the brain through optic nerves.
• Optic nerves: Optic nerves are of two types. These include cones and rods.

1. Cones: Cones are the nerve cells that are more sensitive to bright light. They help in detailed central and colour vision.
2. Rods: Rods are the optic nerve cells that are more sensitive to dim lights. They help in peripheral vision.