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7. What is the probability of a sure event?

8. How many faces a common die has?

8.Find the mean of x, x + 2, x + 4, x + 6, x + 8.

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9.Find the range of the given data : 25, 18, 20, 22, 16, 6, 17, 15, 12, 30, 32, 10, 19, 8, 11, 20

9.Two circles having radii 5 cm and 3 cm intersect each other at two distinct points. If the distance... read more
9.Two circles having radii 5 cm and 3 cm intersect each other at two distinct points. If the distance between their centres is 4 cm, then what is the length of the common chord? read less

1. Define polyatomic ion. Give one example.

Mallela Harish

Lecturer in Chemistry with 6+ years of teaching experience

An ion which has more than one atom is know as polyatomic ion. Polyatomic ion is a group of atoms which has positively or negatively charged. Polyatomic ion is a molecular ion, which has two or more atoms covalently bonded. Examples- Sulphate ion () Ammonium ion ( ) read more

An ion which has more than one atom is know as polyatomic ion.

Polyatomic ion is a group of atoms which has positively or negatively charged.

Polyatomic ion is a molecular ion, which has two or more atoms covalently bonded.

Examples-

Sulphate ion ($SO^{_{4}^{-&space;\ddot{}2}$)

Ammonium ion ( $NH^{_{4}^{+1&space;}}$)

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Mallela Harish

Lecturer in Chemistry with 6+ years of teaching experience

The combinations of elements to form compounds follow some intresting laws, known as "Laws of chemical combinations". They are 1) law of conservations of mass. 2) law of definate proportions 3)law of multiple proportions 4)gay-lussacs law of gaseous volumes 5)avagadro law. 1) Law of conservation... read more

The combinations of elements to form compounds follow some intresting laws, known as "Laws of chemical combinations".

They are

1) law of conservations of mass.

2) law of definate proportions

3)law of multiple proportions

4)gay-lussacs law of gaseous volumes

1) Law of conservation of mass: It was prposed by Antonie Lavoiser. It's states that matter neither can be created nor can be destroyed.It means that The masses of the reactants and products in a chemical reaction will be same.

ex:-

$C&space;+&space;O_{2}&space;\rightarrow&space;CO_{2}$

In the above reaction 12g of carbon (C) is reactiong with 32g of oxygen (O) to form 44g of carbon dioxide ($CO_{2}$) that means 12g+32g =44g.

reactant side mass is 12g+32g =44g & product side mass is 44g.

2) law of constant proportions: It is also know as law of definite proportions. It states that a given compound always have exactly the same proportion of elements by weight, irrespective of the source of the compound.

ex:-

The chemical formula of water is $H_{2}O$.

If you collect the water from tap (or) from sea (or) from rain (or) from a pond, the chemical formula of water remains same as $H_{2}O$.

HARISH MALLELA,

TUTOR PARTNER CHEMISTRY,

URBANPRO.

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5. Find the molecular mass of H2O.

Mallela Harish

Lecturer in Chemistry with 6+ years of teaching experience

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1. Earth attracts apple from the tree and it falls on it but the earth does not move towards the apple. Why?

Mahima Pant

Class 9 Tutor with 2 years of experience

this is because mass of the apple is very small compared to the earth(point sized). Since the mass is negligible , the apple falls towards the earth. But this does not mean that the apple does not attract the earth. As stated in Newton's third law of motion every action has an equal and opposite reaction.... read more

this is because mass of the apple is very small compared to the earth(point sized). Since the mass is negligible , the apple falls towards the earth. But this does not mean that the apple does not attract the earth. As stated in Newton's third law of motion every action has an equal and opposite reaction. Thus as Earth attracts the apple towards it due to gravity the apple also attracts the earth. But since the mass of earth is much larger as compared to that of an apple, we don"t really see the Earth moving towards the apple.

Hope it helps!

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3. Name the force which is required to maintain a body in uniform circular motion?

Mahima Pant

Class 9 Tutor with 2 years of experience

Centripetal force
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