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1g of copper powder was taken in a china dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equation of reactions, the name and the colour of the products formed in each case.

When 1g of copper powder is taken in a china dish and heated, a black-coloured substance is formed. This substance is copper... View Article

Assertion (A): In the process of nuclear fission, the amount of nuclear energy generated by the fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from coal. Reason (R): The nucleus of a heavy atom such as uranium, when bombarded with low-energy neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the product nuclei gets converted to tremendous energy. (a) Both A and R are true and R is correct explanation of the Assertion. (b) Both A and R are true but R is not the correct explanation of the Assertion. (c) A is true but R is false. (d) A is false but R is true.

(a) Both A and R are true and R is correct explanation of the Assertion. Explanation Nuclear Energy 1. It is a... View Article

Assertion (A): Esterification 1s a process m which a sweet smelling substance is produced. Reason (R): When esters relict with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained. (a) Both A and R are true and R is correct explanation of the Assertion. (b) Both A and R are true but R is not the correct explanation of the Assertion. (c) A is true but R is false. (d) A is false but R is true.

(b) Both A and R are true but R is not the correct explanation of the Assertion. Explanation When alcohol... View Article

Incomplete combustion of coal and petroleum : (A) increases air pollution. (B) increases efficiency of machines. (C) reduces global warming. (D) produce poisonous gases. The correct option is : (a) (A) and (B) (b) (A) and (D) (c) (B) and (C) (d) (C) and (D)

(b) (A) and (D) Explanation Coal and petroleum fuels contain carbon molecules on incomplete combustion, they react with atmospheric oxygen... View Article

Which one of the following is responsible for the sustenance of underground water? (a) Loss of vegetation cover (b) Diversion for high water demanding crops (c) Pollution from urban wastes (d) Afforestation

(d) Afforestation Explanation Afforestation is the planting of trees in an ecologically degraded or previously barren environment. Abandoned mines or... View Article

Two bulbs of 100W and 40W are connected in series. The current through the 100W bulb is 1A. The current through the 40W bulb will be: a) 0.4A b) 0.6A c) 0.8A d) 1

d) 1A Given P1=100W,P2=40W in series, i=1A In series , same current will flow in both bulb. A circuit is said to be... View Article

At the time of short circuit, the electric current in the circuit : (a) vary continuouslyn (b) does not change (c) reduces substantially (d) increases heavily

d) increases heavily Explanation When the plastic insulation of live and neutral wires gets torn somehow and touches each other,... View Article

When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is: (a) real (b) inverted (c) virtual and inverted (d) virtual and erect

(d) virtual and erect Explanation A concave mirror is a mirror that is curved inward in the middle. It is... View Article

The laws of reflection hold true for : (a) plane mirrors only (b) concave mirrors only (c) convex mirrors only (d) all reflecting surfaces

(d) all reflecting surfaces Explanation The laws of reflection hold true for all the reflecting surfaces, i.e. all mirrors (either... View Article

The chemical formula of plaster of Paris is a) CaSO4. 2H2O b) CaS04.H2O c) CaS04. 1/2H2O d) 2CaS04.H2O

b) CaSO4.2H2O Explanation The compound plaster of Paris is made by heating gypsum at 120 degree Celsius. The chemical formula... View Article

Baking soda is a mixture of : (a) Sodium carbonate and acetic acid (b) Sodium carbonate and tartaric acid (c) Sodium hydrogen carbonate and tartaric acid (d) Sodium hydrogen carbonate and acetic acid

(c) Sodium hydrogen carbonate and tartaric acid Explanation Baking soda is a mixture of sodium hydrogen carbonate and tartaric acid.... View Article

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution : (A) exchange of atoms takes place(B)exchange of ions takes place(C) a precipitate is produced (D) an insoluble salt is produced The correct option is : (a) (B) and (D) (b) (A) and (C) (c) only (B) (d) (B), (C) and (D)

(d) (B), (C) and (D) Explanation In a double displacement reaction such as the reaction between sodium sulphate solution and... View Article

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a : (a) Combination reaction(b) Displacement reaction (c) Decomposition reaction (d) Double displacement reaction

(d) Double displacement reaction Explanation When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black... View Article

Calcium oxide reacts vigorously with water to produce slaked lime. CaO(s)+H2O(l)→Ca(OH)2(aq) This reaction can be classified as: (A) Combination reaction (B) Exothermic reaction (C) Endothermic reaction (D) Oxidation reaction Which of the following is the correct option?

A and B Explanation CaO(s)+H2O(l)→Ca(OH)2(aq) A combination reaction is a reaction where two or more elements or compounds combine to... View Article

Why is the maximum concentration of pesticides found in human beings?

The maximum concentration of pesticides is found in human beings because humans comprise the topmost level into the food chain,... View Article

List two common signs of sexual maturation in boys and girls.

The common signs of sexual maturation in boys and girls are: (i) Growth of excessive hairs on body parts such... View Article

The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.

The change in magnetic field lines in a coil is the cause of induced electric current in it, and this phenomenon is known as Electromagnetic... View Article

Name a cyclic unsaturated cyclic compound

An example of a cyclic unsaturated compound is Cyclobutene. Explanation Ringed structures called cyclic hydrocarbons may be formed by hydrocarbons. Since... View Article

An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 5 cm. Draw a labelled ray diagram to show the formation of image in this case.

(i) Here the focal length f is 5 cm then 2f will be 10 cm (2×10), and object is placed 10 cm from the lens,... View Article

Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a (i) Spherical lens (ii) Spherical mirror

The relation between the object distance (u), the image distance (v) and the focal length (f) of a spherical mirror (a concave or convex mirror)... View Article

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