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The Fundamental Unit Of Life

Question
CBSEENSC9005208
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Helium atom has an atomic mass of 4 u and has two protons in its nucleus. How many neutrons it have?

Solution

The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus.

Mass of atom =Protons +Neutrons

Since helium atom has a atomic mass of 4 u and it has two protons. Two protons contribute 2 u to atomic mass.
 
4u =2u +Neutrons

Neutrons =4-2 =2

Hence, it must contain 2 neutrons.

Some More Questions From The Fundamental Unit of Life Chapter

Na+ has completely filled K and L-shells. Explain.

If Z = 3, what would be the valency of the element? Also, name the element.

Composition of the nuclei of two atomic species X and Y are given as under


                              X        Y
Protons  =                6        6
Neutrons=                6        6

Give the mass numbers of X and Y. What is the relation between the two species?

For the following statements, write T for True and F for False.

(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

(c) The mass of an electron is about 1/2000 times that of proton.

(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Rutherford’s α-particle scattering experiment was responsible for the discovery of

Isotope of an element has

Number of valence electrons in Cl- ion are

Which one of the following is a correct ? Electronic configuration of sodium

(a) 2, 8,2 (b) 8, 2, 1 (c) 2, 1, 8 (d) 2, 8, 1.

Complete the following Table:


Atomic number

Mass number

Number of neutrons

Number of protons

Number of electrons

Name of the atomic species

9

-

10

-

-

-

16

32

-

-

-

Sulphur

-

24

-

12

-

-

-

2

-

1

-

-

-

1

-

1

0

-

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