Atomic Structure

Samacheer Book Back Questions And Answers For Science Standard 7 Term 1 “Atomic Structure“

I. Choose the appropriate answer:
1. The basic unit of matter is _____.
(a) Element
(b) Atom
(c) Molecule
(d) Electron

2. The subatomic particle revolve around the nucleus is _____.
(a) Atom
(b) Neutron
(c) Electron
(d) Proton

3. _____ is positively charged.
(a) Proton
(b) Electron
(c) Molecule
(d) Neutron

4. The atomic number of an atom is _____.
(a) Number of neutrons
(b) Number of protons
(c) Total number of protons and neutrons
(d) Number of atoms

5. _____ Nucleons comprises of
(a) Protons and electrons
(b) Neutrons and electrons
(c) Protons and neutrons
(d) Neutrons and Positron

II. Fill in the blanks:
1. The smaller particles found in the atom is called _____.
2. The nucleus has _____ and _____.
3. The _____ revolve around the nucleus.
4. If the valency of carbon is 4 and that of hydrogen is 1, then the molecular formula of methane is _____.
5. There are two electrons in the outermost orbit of the magnesium atom. 6. Hence, the valency of magnesium _____.

Answers:
1. Sub-atomic particles
2. Protons, Neutrons
3. Electrons
4. CH₄
5. 2

III. Match the following:
1. Valency                                 A. Fe
2. Neutral Particle                     B. Proton
3. Iron                                       C. Electrons in the outermost Orbit
4. Hydrogen                              D. Neutron
5.Positively charged Particle     E. Monovalent

Answers:
1. C
2. D
3. A
4. E
5. B

IV. True or False. If False, give the correct statement (T/F):
1. The basic unit of an element is molecule.
2. The electrons are positively charged.
3. An atom is electrically neutral.
4. The nucleus is surrounded by protons.

Answers:
1. False (The basic unit of an element is atom)
2. False (The electrons are negatively charged)
3. True
4. False (The nucleus is surrounded by electrons)

V. Complete the analogy:
1. Sun: Nucleus, planets: _____.
2. Atomic number: _____ Mass number: number of protons and neutrons.
3. K: Potassium, C: _____.

Answers:
1. Electrons
2. Number of protons
3. Carbon

VI. Assertion and reason:
1. Assertion: An atom is electrically neutral.
Reason: Atoms have equal number of protons and electrons.
2. Assertion: The mass of an atom is the mass of nucleus.
Reason: The nucleus is at the centre.
3. Assertion: The number of protons and neutrons is atomic number.
Reason: The mass number is sum of protons and neutrons.

Answers:
1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
2. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
3. Assertion is false but the reason is true statement.
(The number of protons and neutrons is mass number)

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