Std 10th Science Part 1 – Chapter 2 : Periodic Classification of Elements Exercise Questions And Answers Maharashtra Board

Q1. Rearrange the columns 2 and 3 so as to match with the column 1.

Column 1	Column 2	Column 3
i. Triad	a. Lightest and negatively charged particle in all the atoms	1. Mendeleev
ii. Octave	b. Concentrated mass and positive charge	2. Thomson
iii. Atomic number	c. Average of the first and the third atomic mass	3. Newlands
iv. Period	d. Properties of the eighth element similar to the first	4. Rutherford
v. Nucleus	e. Positive charge on the nucleus	5. Dobereiner
vi. Electron	f. Sequential change in molecular formulae	6. Moseley

Answer –

Column 1	Column 2	Column 3
i. Triad	c. Average of the first and the third atomic mass	5. Dobereiner
ii. Octave	d. Properties of the eighth element similar to the first	3. Newlands
iii. Atomic number	e. Positive charge on the nucleus	6. Moseley
iv. Period	f. Sequential change in molecular formulae	1. Mendeleev
v. Nucleus	b. Concentrated mass and positive charge	4. Rutherford
vi. Electron	a. Lightest and negatively charged particle in all the atoms	2. Thomson

Q2. Choose the correct option and rewrite the statement.

a. The number of electrons in the outermost shell of alkali metals is……

(i) 1 (ii) 2 (iii) 3 (iv) 7

Answer – (i) 1

Statement: The number of electrons in the outermost shell of alkali metals is 1.

b. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in …..

(i) Group 2 (ii) Group16 (iii) Period 2 (iv) d-block

Answer – (i) Group 2

Statement: Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in Group 2.

c. Molecular formula of the chloride of an element X is XCl. This compound is a solid having high melting point. Which of the following elements be present in the same group as X.

(i) Na (ii) Mg (iii) Al (iv) Si

Answer – (i) Na

Statement: Molecular formula of the chloride of an element X is XCl. This compound is a solid having high melting point. The element that would be present in the same group as X is Na.

d. In which block of the modern periodic table are the nonmetals found?

(i) s-block (ii) p-block (iii) d-block (iv) f-block

Answer – (ii) p-block

Statement: In the modern periodic table, the nonmetals are mainly found in the p-block.

Q3. An element has its electron configuration as 2,8,2. Now answer the following questions.

a. What is the atomic number of this element?

The atomic number is the total number of electrons:
2+8+2=12.

b. What is the group of this element?

Since it has 2 valence electrons (in the outermost shell), it belongs to Group 2.

c. To which period does this element belong?

Since the electrons are filled in three shells (K, L, M), it belongs to the Period 3.

d. With which of the following elements would this element resemble? (Atomic numbers are given in the brackets) N (7), Be (4), Ar (18), Cl (17)

The element (atomic number 12, Magnesium) will resemble Be (Beryllium, atomic number 4).
Reason: Elements in the same group have similar chemical properties. Beryllium (Be), with a configuration of (2, 2), also has 2 valence electrons, placing it in Group 2, like the element in the question.

Q4. Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.

Element (Atomic No.)	Electronic Configuration
Li (3)	2, 1
Si (14)	2, 8, 2004
He (2)	2
Na (11)	2, 8, 2001
P (15)	2, 8, 2005
H (1)	1
N (7)	2, 5
Ca (20)	2, 8, 8, 2
S (16)	2, 8, 2006
Be (4)	2, 2
Ar (18)	2, 8, 2008
C (6)	2, 4
O (8)	2, 6
B (5)	2, 3
Al (13)	2, 8, 2003
F (9)	2, 7

a. ₃Li,₁₄Si,₂He,₁₁Na,₁₅P. Which of these elements belong to the period 3?

Answer: ₁₄Si (2, 8, 4), ₁₁Na (2, 8, 1), and ₁₅P (2, 8, 5).
Explanation: Elements whose electrons are filled in three shells (K, L, M) belong to Period 3.

b. ₁H,N,₂₀Ca,₁₆S,₄Be,₁₈Ar. Which of these elements belong to the second group?

Answer: ₂₀Ca (2, 8, 8, 2) and ₄Be (2, 2).

Explanation: Elements belonging to a group have the same number of valence electrons. Group 2 elements (alkaline earth metals) have 2 electrons in their outermost shell.

c. ₇N,₆C,₈O,₅B,₁₃Al. Which is the most electronegative element among these?

Answer: O (Oxygen).
Explanation: Electronegativity (nonmetallic character) generally increases from left to right across a period. The elements B (5), C (6), N (7), O (8) are in Period 2. Oxygen (O) is farthest to the right, making it the most electronegative among these.

d. ₄Be,₆C,₈O,₅B,₁₃Al. Which is the most electropositive element among these?

Answer: ₁₃Al (Aluminium).

Explanation: Electropositivity (metallic character) generally decreases from left to right across a period. Beryllium (Be) and Aluminium (Al) are metals. Al is in Period 3, while Be, C, O, and B are in Period 2. Since metallic character increases down a group, and Al is the metal farthest to the left of its period among the options, Al is the most electropositive.

e. ₁₁Na,₁₅P,₁₇Cl,₁₄Si,₁₂Mg. Which of these has the largest atom?

Answer: ₁₁Na (Sodium).
Explanation: All these elements belong to Period 3. Across a period (from left to right), the atomic size generally decreases because the increasing nuclear charge pulls electrons closer. Sodium (Na) is the element farthest to the left in this group, so it has the largest atomic size.

f. ₁₉K,₃Li,₁₁Na,₄Be. Which of these atoms has the smallest atomic radius?

Answer: ₄Be (Beryllium).
Explanation:
- Li and Be are in Period 2; Na and K are in Group 1.
- Atomic size increases down a group (Li<Na<K).
- Atomic size decreases across a period (Li>Be).
- Therefore, Beryllium (Be), which is the smallest in its period, is the smallest overall.

g. ₁₃Al,₁₄Si,₁₁Na,₁₂Mg,₁₆S. Which of the above elements has the highest metallic character?

Answer: ₁₁Na (Sodium).
Explanation: All these elements are in Period 3. Metallic character is highest on the left side of the period and decreases to the right. Sodium (Na) is the leftmost element listed, meaning it has the highest metallic character (electropositivity).

h. ₆C,₃Li,₉F,₇N,₈O. Which of the above elements has the highest nonmetallic character?

Answer: ₉F (Fluorine).

Explanation: Nonmetallic character (electronegativity) increases from left to right across a period. Fluorine (F) is the farthest right element in Period 2 (before the inert gas Ne) among those listed, so it is the most nonmetallic.

Q5. Write the name and symbol of the element from the description

a. The atom having the smallest size.

Answer: Helium (He).

b. The atom having the smallest atomic mass.

Answer: Hydrogen (H).

c. The most electronegative atom.

Answer: Fluorine (F) (It’s generally known as the most electronegative element, also evident from its position farthest right in its period before the noble gases ).

d. The noble gas with the smallest atomic radius.

Answer: Helium (He).

e. The most reactive nonmetal.

Answer: Fluorine (F).

Q6. Write short notes.

a. Mendeleev’s periodic law.

Statement: The physical and chemical properties of elements are a periodic function of their atomic masses.
Explanation: Mendeleev arranged the 63 known elements based on increasing atomic mass, noting that elements with similar properties appeared regularly (periodically). This led him to state his law.

b. Structure of the modern periodic table.

Arrangement: Elements are arranged in an increasing order of their atomic numbers.
Groups (Vertical Columns): There are 18 vertical columns called groups. Elements within a group have the same number of valence electrons and thus show similarity and gradation in chemical properties.
Periods (Horizontal Rows): There are 7 horizontal rows called periods. The number of shells containing electrons determines the period. Properties change slowly from one end to the other across a period.
Blocks: The table is divided into four blocks: s-block (Groups 1 and 2), p-block (Groups 13-18), d-block (Groups 3-12, also called transition elements), and f-block (lanthanide and actinide series at the bottom).

c. Position of isotopes in the Mendeleev’s and the modern periodic table.

Mendeleev’s Periodic Table:
- Isotopes were discovered later, after Mendeleev put forth his table.
- Since isotopes have different atomic masses but the same chemical properties , placing them in his table posed a challenge and an ambiguity.
Modern Periodic Table:
- This table is based on atomic number (Z), which is a more fundamental property.
- Isotopes have the same atomic number, so they are naturally accommodated in the same position in the modern periodic table. The ambiguity faced by Mendeleev is removed.

7. Write scientific reasons.

a. Atomic radius goes on decreasing while going from left to right in a period.

Reason: When moving from left to right in a period, the electrons are added to the same outermost shell.
However, the atomic number increases by one at a time, meaning the positive charge (nuclear charge) on the nucleus increases.
This increased positive nuclear charge pulls the electrons towards the nucleus more strongly, causing the atomic size to decrease.

b. Metallic character goes on decreasing while going from left to right in a period.

Reason: Metallic character is the tendency of an atom to lose valence electrons (electropositivity).
Moving from left to right, the effective nuclear charge increases and the atomic radius decreases.
This makes the attractive force holding the valence electrons stronger , so the atom’s tendency to lose electrons (metallic character)decreases.

c. Atomic radius goes on increasing down a group.

Reason: When moving down a group, a new electronic shell gets added at each step.
This addition of a new shell increases the distance between the outermost electron and the nucleus.
Consequently, the overall atomic size increases.

d. Elements belonging to the same group have the same valency.

Reason: The valency of an element is determined by the number of valence electrons (electrons in the outermost shell).
Elements within the same group of the periodic table have the same number of valence electrons.
Therefore, since their capacity to combine (valency) is the same, they have the same valency.

e. The third period contains only eight elements even though the electron capacity of the third shell is 18.

Reason: Although the third shell (M shell) has a maximum electron capacity of 18 (2n²) , the
Law of Electron Octet dictates the filling of electrons in certain elements.
The outermost shell can only hold a maximum of 8 electrons, so the third period finishes filling at
8 elements to achieve a stable octet (like Argon, Ar, with configuration 2, 8, 8).

8. Write the names from the description.

a. The period with electrons in the shells K, L and M.

Answer : Third Period

(Because it has three occupied shells: K, L, and M) .

b. The group with valency zero.

Answer : Group 18 (Noble Gases)

(Because their outermost shell is complete, so their valency is zero) .

c. The family of nonmetals having valency one.

Answer : Halogen family (Group 17).

d. The family of metals having valency one.

Answer : Group 1 (Alkali Metals).

e. The family of metals having valency two.

Answer : Group 2 (Alkaline Earth Metals).

f. The metalloids in the second and third periods.

Answer : Boron (B), Silicon (Si).

g. Nonmetals in the third period.

Answer : Phosphorus (P), Sulfur (S), Chlorine (Cl), Argon (Ar).

h. Two elements having valency 4.

Answer : Carbon (C), Silicon (Si).