For a common man, pure substance that it is not adulterated. for example, for a common man, pure milk means the liquid material that is given by cow or buffallo and it is not mixed with water or other materials to thicken it. But for a chemist, any milk is not a pure substance. Milk is a mixture of water, fats and proteins. These materials are different in milk obtained from different source. Similarly, pure fruit juice for a common man means that it is not mixed with fruit juice of other fruits water or salt. But for a chemist, any fruit juice is a mixture of water and several other substances. For a common man pure gold means gold of a given composition. But a chemist known that no ornaments can be made from pure gold. All ornaments of gold contain gold and copper.

As we know,\(F=\cfrac { G{ m }_{ 1 }{ m }_{ 2 } }{ { 4r }^{ 2 } } \)
According to question, r' = 6r
So, \(F=\cfrac { G{ m }_{ 1 }{ m }_{ 2 } }{ \left( 6r \right) ^{ 2 } } =\cfrac { G{ m }_{ 1 }{ m }_{ 2 } }{ 36r^{ 2 } } =\cfrac { F }{ 6 } \)
To maintain same force one of the mass is to be increased by 36 times.

Indigenous varieties of bee
(i) Apis cerana indica (Indian bee)
(ii) Apis dorsata F.(rock bee)
(iii) A.Florae F.(little bee)
Exotic variety
Apis mellifera(Italian bee)

Methods of Weed Control:
(i) Mechanical method: In this method, weed plants are removed from the field either manually or with the help of agricultural implements. For example, uprooting or hand hoeing, weeding with khurpi, ploughing ect.
(ii) Cultural method: This includes:
(a) proper seed bed preparation,
(b) timely sowing of crops,
(c) intercropping, and
(d) crop rotation.
(iii) Chemical methods: Weeds can be controlled by spraying chemicals which do not harm crop plants but destroy weed plants.These chemicals are weedicides e.g., 2, 4-D, atrazine, fluchloralin.
(iv) Biological method: There are particular organisms which feed on particular weed. for example, Cochineal insect can be introduced in the water body to control aquatic weeds.

No.	Source	Nutrients
1.	Air	Carbon (in the form of CO2), oxygen by exchange of gas through  stomata.
2.	Water	Hydrogen (in the form )
3.	Soil	(i) Macro-nutrients  Nitrogen, Phosphorus, Potassium, Sulphur, Calcium, Magnesium.  (ii) Micro-nutrients  Iron, Manganese, Boron, Zinc, Copper, Molybdenum, Chlorine.

The concentration of carbon dioxide in the atmosphere is increasing due to the current global trend of deforestation and increasing combustion of fossil fuels. A part of the sunlight incident on the earth reflected back in the form of infrared radiations. This infrared radiation are absorbed by the carbon dioxide molecules. hence, the envelope of CO₂  of the atmospheric air would be able to trap larger proportion of the infrared radiations if the concentration of CO₂ is increased, thereby heating the atmosphere.
This heating of the absorption of infrared earth's temperature and may cause melting of glacier and thereby flooding the coastal plains.
Greenhouse gases:
(i) CO₂ , 
(ii) Methane (CH₄ ) and
(iii) Nitrogen oxide.

(i) Immediate cause of disease is Infectious organisms like virus, bacteria, fungi, protozoan etc.For example, the cause of loose motions can be an infection with a virus, Here viruses is the immediate cause of disease.
(ii) Contributory cause of disease:
(a) poor health due to lack of good nourishment.
(b) poor economic condition due to which one does not get proper and sufficient food and lives in unhygienic conditions.
(c) genetic defects which cause some people more prone to disease than others.
(d) Lack of public services.

We know, moment p = mv
Kinetic energy, k = 1/2mv² = (mv)²/2m = p²/2m
For same p, \(k\alpha \frac { 1 }{ m } \Rightarrow \frac { { k }_{ 1 } }{ { k }_{ 2 } } =\frac { { m }_{ 2 } }{ { m }_{ 1 } } \)
If m₁2 , then k₁>k₂
Thus, the lighter object has more kinetic energy than the heavier body.

The second equation of motion. Suppose a body starts with initial velocity u and due to uniform acceleration a,its final velocity becomes v after t. Then
Average velocity=\(\frac { Intial\quad velocity+Final\quad velocity }{ 2 } =\frac { u+v }{ 2 } \)
So, the distance covered by the body in time t is
s = Average velocity x Time
= \(\frac { u+v }{ 2 } \) x t = \(=\frac { u+(u+at) }{ 2 } Xt\)   \([\therefore v=u+at]\)
\(=\frac { 2ut+at^{ 2 } }{ 2 } \)
or \(s=ut+\frac { 1 }{ 2 } at^{ 2 }\) 

Bone	Cartilage
1. Bone is inflexible and hard.	1. Cartilage is usually flexible or elastic and soft.
2. Its matrix contains protein ossein and calcium phosphate.	2. The matrix of the cartilage contains protein chondrin and usually lacks calcium.
3. Bone cells (i.e., osteocytes) have irregular outlines due to the presence of a number of protoplasmic outgrowths.	3. The cells of cartilage, chondrocytes, are oval in outline.
4. The lacunae (cavities or spaces) are provided with numerous fine branches called canaliculi.	4. The canaliculi are absent.
5. Its matrix shows concentric lamellae.	5. Matrix is homogeneous.
6. Bone has Haversian canals and the marrow cavity.	6. Cartilage is devoid of such structures.

(i)After one half-life period, the amount of isotope becomes half\(\left(1\over2\right)\).
(ii)After second half-life, the amount of isotope becomes \({1\over 4}th\) (half of half, i.e., \({1\over2}\times{1\over 2}={1\over4}\) ).
(iii)After third half-life, the amount of isotopes remains \(={1\over2}\times{1\over 4}={1\over 8}\)th of the original amount.
(iv)After the fourth half-life, the amount of isotopes remains \(={1\over2}\times{1\over 8}={1\over 16}th\)of the original amount.
Thus, \({1\over 16}\) of the original radioisotope would be left behind after four half-life periods or 3600 seconds.

1 u = 1/12th of 1 atom of C-12
1 mole C-12 = 12 gram
12 gram C-12 = 6.022 x 10²³ atoms
or  6.022 x 10²³ atoms of C-12 = 12 grams
One atom of C-12 = \(\frac { 12 }{ 6.022\times { 10 }^{ 23 } } \)g
1 u = \(\frac { 12 }{ 6.022\times { 10 }^{ 23 } } \times \frac { 1 }{ 12 } \)
= 1.660302 x 10^-24 gram.

A compound is a substance which is formd by the combination of two or more elements in a fixed proportion by weight. The properties of a compound are entirely different from its constituent. A compound can be decomposed into two or more simpler substances. For example, water is a compound formed by combination of 89% oxygen and 11% hydrogen by weight irrespectively of its source. Its properties namely, density, physical state, reactivity etc. are quite different from the properties of hydrogen and oxygen. Water can be oxygen, salt is made of sodium and chlorine and sugar is made of carbon, oxygen and hydrogen having their constituent elements in fixed proportions. Carbon dioxide, salt and sugar are compounds.