"AKC SCIENCE CLASSES"
CLASS 09 TH (CBSE AND MP BOARD)
CHAPTER 04
STRUCTURE OF THE ATOM
EXERCISES QUESTIONS AND ANSWERS
(PART 02)
Q.11:- The average atomic mass of a sample of element X is 16.2 u. What are the percentage of isotopes ¹⁶₈X and ¹⁸₈X in the sample?
Ans:- Let the percentage of X-16 isotope = x
∴ The percentage of X-18 isotope = (100-x)
From the information, the average atomic mass of the element X is
x × 16 (100 - x) × 18
= ------- = ----------------
100 100
But the given atomic mass of the element X = 16.2 u
x × 16 (100 - x) × 18
= ------- = ---------------- = 16.2
100 100
16x + 1800 -18x = 16.2 × 100 = 1620
-2x = 1620 -1800 = -180, x = 180/2 = 90
Percentage of X-16 isotope = 90,
Percentage of X-18 isotope = 10
Q.12:- If Z = 3, what would be the valency of the element? Also, name the element.
Ans:- The configuration of the element with Z = 3 is K(2) L(1). It has one electron in the valence shell i.e., L-shell. Its valency is one. The element is lithium (Li).
Q.13:- Composition of the nuclei of two atomic species X and Y are given as under
X Y
Protons = 6 6
Neutrons = 6 8
Give the mass number of X and Y. What is the relation between the two species?
Ans:- Mass number of X = protons + neutrons = 6 + 6 = 12
Mass number of Y = protons + neutrons
= 6 + 8 = 14
The species X and Y are the isotopes because their atomic numbers are same and their mass numbers are different.
Q.14:- 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.
Ans:- False
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
Ans:- False
(c) The mass of an electron is about 1/2000 times that of proton.
Ans:- True
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Ans:- False.
Q.15:- Rutherford's alpha-particle scattering experiment was responsible for the discovery of
(a) Atomic Nucleus
(b) Electron
(c) Proton
(d) Neutron
Ans:- (a) Atomic Nucleus.
Q.16:- Isotopes of element have :-
(a) the same physical properties.
(b) different chemical properties.
(c) different number of neutrons.
(d) different atomic numbers.
Ans:- (c) different number of neutrons.
Q.17:- Number of valence electrons in Cl⁻ ions are :-
(a) 16
(b) 8
(c) 17
(d) 18.
Ans:- (d) Cl⁻ ion has 18 electrons (17 + 1).
Q.18:- Which one of the following is a correct electronic configuration of sodium?
(a) 2,8
(b) 8,2,1
(c) 2,1,8
(d) 2,8,1
Ans:- (d) is the correct answer.
Q.19:- Complete the following table.
Ans:- First Line :- Mass number
= Atomic number (9) + No. of neutrons (10) = 19
No. of protons = Atomic number = 9
No. of electrons = Atomic number = 9
Name of species = Fluorine (F)
Second Line :- No. of neutrons
= Mass number (32) - Atomic number (16) = 16
No. of protons = Atomic number = 16
No. of electrons = Atomic number = 16
Third Line :- Atomic number
= No. of protons = 12
No. of neutrons
= Mass number (24) - Atomic number (12) = 12
No. of electrons = Atomic number = 12
Name of species = Magnesium (Mg)
Fourth Line :- Atomic number
= No. of protons = 1
No. of neutrons
= Mass number (2) - Atomic number (1) = 1
No. of electrons = Atomic number = 1
Name of species = Deuterium (D)
Fifth Line :- Atomic number = No. of protons = 1
No. of electrons = Atomic number = 1
Name of species = protium or hydrogen (H)
The complete table can also be represented as :-
SCIENCE || CLASS 09TH || CHAPTER 04 || EXERCISE QUESTIONS AND ANSWERS || PART 01 || CBSE AND MP BOARD CLICK HERE.
SCIENCE || CLASS 09TH || CHAPTER 04 || BASIC CONCEPTS || CBSE AND MP BOARD CLICK HERE
SCIENCE || CLASS 09TH || CHAPTER 04 || INTEXT QUESTIONS AND ANSWERS || CBSE AND MP BOARD CLICK HERE
