Page 59 - Science Class 07

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i Matter can exists in any of the three physical states— solid, liquid or gas.
i Elements can be further divided into metals, non-metals and metalloids.
i There are about 22 non-metals out of which 11 are gases.
i Atoms can neither be created nor be destroyed.

i Sometimes, two or more atoms of an element combine to form more stable molecule, e.g,
oxygen.
i Components of a mixture can also be separated by a physical or chemical method.
i In a heterogeneous mixture, components are easily visible.

i In a homogeneous mixture, all the components are properly mixed through out the sample.
i Water is a compound of hydrogen and oxygen in the ration of 2:1.
i If one molecule of an element contains two atoms they are called diatomic.

i Chemical equation is a representation of chemical reaction with the help of chemical
symbols and formulae.

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A. Tick (3) the correct op on.
1. How many elements have been found so far?
(a) 96 (b) 106
(c) 115 (d) 206

2. Which of the following is not a property of metal?
(a) Duc lity (b) Malleability
(c) Conduc vity (d) Low boiling point

3. Which of the following is not a non-metal?
(a) Carbon (b) Sulphur
(c) Iodine (d) Mercury
4. Which of the following is a metalloid?

(a) Phosphorous (b) Silver
(c) Carbon (d) Silicon
5. Sugar is a compound of carbon, hydrogen and oxygen in the ra o _______ respec vely.
(a) 12 : 22 : 11 (b) 14 : 16 : 18

(c) 2 : 6 : 4 (d) 12 : 18 : 22
B. Fill in the blanks.
1. Ma er can exist in _____________ physical states.
2. A chemical change is also known as _____________ .

3. The chemical formula of reactant is wri en on _____________ .

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