When the two terminals of battery are combined with negative and positive electrodes which are immersed in water, the water is dissociated into its components oxygen and hydrogen. Oxygen is collected on positive electrode and hydrogen is collected on negative electrode.

Friction is called a necessary evil because we cannot do anything without friction and it also shows effects. No movement would come to an end without friction. No body would rest without friction. We cannot write with pen or pencil if there is no friction. If an object starts moving, it would never stop if there was no friction. It is also necessary for grip and bringing movements to rest.

Water can be made safe for drinking by following ways:
(i) Water is filtered. Many filters available in the markets are used by people.
(ii) Some use boiling as a method for obtaining safe drinking water because boiling kills the germs present in the water.
(iii) Chlorination is a chemical method for purifying water.

Stars are present both during day time as well as during night time. Because of the bright light of the Sun, the stars are not visible during day time.

Because the area of pointed end of the nail is much smaller than that of its head. The same force, therefore produces a pressure sufficient to push the pointed end of the nail into the wooden plank.

The body produce antibodies when a disease carrying microbe enters in it. The body also retains memory of this encounter to fight the microbe if it enters again. A vaccine consists of dead or weakened microbes which when introduced in a healthy body, produce suitable antibodies to fight and kill themselves. These antibodies remain in the body to protect it from disease causing microbes thus develop immunity.

Water is essential for plants. It helps in germination of seeds because seeds cannot germinate under dry conditions. Nutrients dissolves in water get transported to each part of the plant. It protects the crop from frost and hot air currents. Water is important for proper growth and development of flowers, fruits and seeds of plants. Along with water, minerals and fertilizers are also absorbed. Plants contain nearly 90% water. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season.

False, we can survive for some time without food but we cannot survive even for a few minutes without air.

Rayon is made from cellulose obtained from wood pulp. Nylon, polyester and acrylic are made entirely of chemicals. Nylon, polyester are made up of repeating units of amides and esters respectively

The advantages of using CNG and LPG as fuels are as follows :
(i) CNG and LPG are clean fuels.
(ii) They do not produce pollution.
(iii) They are easily available.
(iv) They can be used directly for burning.
(v) They are easy to transport.
(vi) Their cost is low.

Beneficial effects of bacteria are as follows :
(i) They give us various milk products like curd and cheese
(ii) They cause immune enhancement and prevents intestinal disorders
(iii) They decompose organic matter to give nutrients to plants.

Advantages of using chemical fertilisers over manures are
(i) Fertilisers are nutrient specific and provide specific nutrient to soil in desired quantity.
(ii) These, being readily soluble in water, can be absorbed easily by the crop plants. If it is used in excess, it causes tremendous changes in the chemical nature of soil and makes it less fertile.

Microorganisms are harmful for human beings in many ways. They cause diseases in humans, plants and animals, e.g.
(i) In humans, bacteria cause diseases such as cholera, typhoid, tuberculosis, etc.
(ii) In cattle, the foot and mouth disease is caused by a virus.
(iii) Also several microbes cause diseases in plants, e.g. tikka disease, late blight of potato. Some microbes grow on food and secrete toxic substances which make the food poisonous.

Threshing - The process in which the grain seeds are separated from chaff is called
threshing. This is carried out with the help of a machine called combine that is a combination of a harvester and thresher.

Preparation of soil - It is the first step before sowing the crop. In this, the soil is ploughed to loosen it and make it aerated which allows the roots to breathe easily. This also helps earthworms and microbes in the soil that bring the nutrient rich soil to the top. The process of loosening and turning of soil is called tilling or ploughing, which is followed by levelling and manuring.