Grade-10-Chemistry-Olympiad: Modern Periodic Table & Periodic ... - Free Printable

Let's solve each multiple-choice question from the worksheet and explain the reasoning behind the correct answers.

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Question (1):

The modern form of the periodic table is divided into groups and periods. On descending a group in the periodic table we find that:
(A) Electronegativity of element increases
(B) Ionisation energy of elements increases
(C) Metallic character of elements increases
(D) Size of elements decreases

#### ✔ Correct Answer: (C) Metallic character of elements increases

#### Explanation:
As we move down a group:
- The number of electron shells increases → atomic size increases.
- The outer electrons are farther from the nucleus → less tightly held → easier to lose electrons.
- This leads to an increase in metallic character (since metals tend to lose electrons).
- Electronegativity decreases (less ability to attract electrons).
- Ionisation energy decreases (easier to remove electrons).
- Atomic size increases, not decreases.

So, only option (C) is correct.

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Question (2):

Periods are the horizontal rows that are present in the modern form of the periodic table. Which of the following properties generally show a decreasing trend along a period?

(A) Atomic size
(B) Electron affinity
(C) Ionisation energy
(D) Electronegativity

#### ✔ Correct Answer: (A) Atomic size

#### Explanation:
Moving from left to right across a period:
- Nuclear charge increases.
- Electrons are added to the same shell, so shielding effect remains almost constant.
- Increased effective nuclear charge pulls electrons closer → atomic size decreases.
- Ionisation energy generally increases (but has exceptions).
- Electron affinity generally increases (with exceptions).
- Electronegativity increases across a period.

Hence, only atomic size shows a clear decreasing trend.

> So, (A) is correct.

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Question (3):

The idea of the periodic table was to classify the different elements that are present in this Universe. Elements are classified:
(i) To correlate their properties with some fundamental property
(ii) To study the elements better
(iii) To find relationship among elements
(iv) To formulate a table

Options:
(A) (i) only
(B) (i), (ii) & (iii)
(C) (i) & (ii)
(D) All of these

#### ✔ Correct Answer: (D) All of these

#### Explanation:
The purpose of the periodic table includes:
- Organizing elements based on atomic number (a fundamental property) → (i)
- Making it easier to study elements and predict behavior → (ii)
- Revealing trends and relationships between elements → (iii)
- Creating a systematic table for representation → (iv)

All four reasons are valid purposes of classification.

Thus, (D) All of these is correct.

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Question (4):

Demetri Mendeleev was a Russian Scientist who first gave the idea about a Periodic Table. Which of the following are the demerits of Mendeleev's periodic table?
(i) No proper position for hydrogen is given

*(Note: Only one option is listed here; likely more options were meant to be included, but only (i) appears.)*

However, based on standard knowledge, the demerits of Mendeleev’s periodic table include:
- No fixed position for hydrogen – it resembles both alkali metals and halogens.
- Positions of isotopes not explained.
- Some elements placed out of order based on atomic mass (e.g., Ar and K).
- No place for noble gases initially.

But since only (i) is listed as an option, and it is indeed a demerit, the answer would be:

#### ✔ Answer: (i) No proper position for hydrogen is given
→ This is true and one of the major limitations of Mendeleev's table.

If this were a multiple-select format, other demerits could be added. But as per the given choice, (i) is correct.

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✔ Final Answers Summary:

| Question | Correct Answer |
|--------|----------------|
| (1) | (C) Metallic character increases |
| (2) | (A) Atomic size |
| (3) | (D) All of these |
| (4) | (i) No proper position for hydrogen |

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