Chemistry MCQs
Topic Notes: Chemistry
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
11
What atomic property of carbon contributes to its ability to form exceptionally strong bonds?
Answer:
small
Carbon has a small atomic radius, which allows the nucleus to exert a strong attraction on shared bonding electrons. This proximity leads to shorter, stronger covalent bonds compared to larger atoms in the same group. The small size also facilitates effective orbital overlap, which is essential for the stability of the carbon-carbon bonds found in organic molecules.
12
On what basis did Mendeleev organize the periodic nature of element properties in his periodic table?
Answer:
Atomic mass
Mendeleev's Periodic Law stated that the properties of elements are a periodic function of their atomic masses. He arranged elements in order of increasing atomic mass, which allowed him to predict the existence and properties of elements that had not yet been discovered at that time.
13
Which of the following halogen atoms possesses the largest atomic diameter?
Answer:
iodine
Atomic radius increases down a group in the periodic table due to the addition of successive electron shells. Among the halogens (Group 17), iodine is located furthest down the group, resulting in the largest atomic radius and diameter compared to fluorine, chlorine, and bromine.
14
Which of the following sets of elements constitutes a valid Dobereiner triad?
Answer:
Li, Na, K
Johann Wolfgang Dobereiner identified groups of three elements, known as triads, where the atomic mass of the middle element is approximately the average of the other two. The triad of Lithium (Li), Sodium (Na), and Potassium (K) is a classic example, where the atomic mass of sodium is roughly the mean of the atomic masses of lithium and potassium.
15
How does the atomic size change when an electron is removed to form a cation versus when an electron is added to form an anion?
Answer:
Size decreases and increases respectively
Removing an electron reduces electron-electron repulsion and increases the effective nuclear charge per electron, causing the radius to decrease (cation formation). Adding an electron increases electron-electron repulsion and shields the outer electrons more effectively, leading to an increase in the ionic radius (anion formation).
16
How are elements arranged in the modern periodic table?
Answer:
In increasing order of atomic numbers
The modern periodic table arranges elements in increasing order of their atomic numbers (the number of protons). This arrangement corrects the anomalies found in Mendeleev's table, which was based on atomic mass, and aligns elements with similar electronic configurations in the same groups.
17
Among the following elements, which one has the largest atomic radius?
Answer:
Al
In a period, atomic radius decreases from left to right due to increasing effective nuclear charge. Aluminum (Al), Silicon (Si), Phosphorus (P), and Sulfur (S) are all in the third period. Since Al is the leftmost element among these, it has the largest atomic size.
18
Which physical property consistently increases as the atomic number increases within both Group 1 (alkali metals) and Group 17 (halogens) of the periodic table?
Answer:
Atomic size
Atomic size is defined by the distance from the nucleus to the outermost electron shell. As one moves down a group in the periodic table, the principal quantum number (n) increases, adding new electron shells. This increase in the number of shells results in a larger atomic radius, a trend that holds true for both the alkali metals in Group 1 and the halogens in Group 17.
19
Among the following elements, which one possesses the largest atomic radius?
Answer:
Li
Atomic radius generally decreases across a period from left to right due to increasing effective nuclear charge. Lithium (Li) is in Period 2, Group 1, while Oxygen (O) and Fluorine (F) are further to the right in the same period. Hydrogen (H) is in Period 1. Therefore, Lithium has the largest atomic radius among these choices.
20
Which of the following atomic radii definitions typically reflects the largest size for a given atom?
Answer:
Vander Walls' radius
Van der Waals' radius is defined as half the distance between the nuclei of two non-bonded atoms in adjacent molecules. Because it involves weak intermolecular forces rather than chemical bonds, it is significantly larger than covalent or metallic radii, which involve closer electron sharing or delocalization.