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
81
Match the following groups of elements with their respective classifications: (a) Group IA, (b) Group zero, (c) d-block, (d) f-block.
Answer:
a-2, b-1, c-4, d-3
Group IA elements are alkali metals. Group zero (Group 18) elements are inert gases. Elements in the d-block are classified as transition elements, and elements in the f-block are known as inner-transition elements (lanthanides and actinides). Therefore, the correct mapping is a-2, b-1, c-4, d-3.
82
Elements belonging to the same group in the modern periodic table share which common characteristic?
Answer:
valence electrons
Elements in the same vertical column (group) of the modern periodic table exhibit similar chemical properties because they possess the same number of valence electrons in their outermost shells, leading to similar bonding behaviors and reactivity patterns.
83
In the modern periodic table, which period contains elements with atomic numbers ranging from 11 to 14?
Answer:
3
Elements with atomic numbers 11 (Sodium), 12 (Magnesium), 13 (Aluminum), and 14 (Silicon) all belong to the third period. The third period begins with the filling of the 3s orbital after the completion of the second period (which ends at atomic number 10, Neon). These elements are characterized by having their valence electrons in the third principal energy level.
84
Which period in the modern periodic table contains exactly 32 elements?
Answer:
Period 6
The sixth period of the periodic table includes the lanthanide series, which accounts for the addition of 14 elements beyond the standard representative elements. Consequently, the total number of elements in Period 6 is 32, filling the 6s, 4f, 5d, and 6p orbitals.
85
Up to which element was Newlands' Law of Octaves considered applicable?
Answer:
calcium
John Newlands proposed the Law of Octaves, which stated that every eighth element exhibits properties similar to the first, analogous to musical octaves. However, this empirical observation was found to be valid only for lighter elements up to calcium (atomic number 20). Beyond calcium, the inclusion of transition metals disrupted the pattern, rendering the law ineffective for heavier elements in the periodic table.
86
Which metal produces a characteristic yellow flame when subjected to a flame test?
Answer:
sodium
In a flame test, the excitation of electrons in metal ions produces characteristic emission spectra. Sodium ions (Na+) emit a strong, persistent yellow light at approximately 589 nm, which is a standard diagnostic test for the presence of sodium in a sample.
87
In the modern periodic table, which period contains only gaseous elements?
Answer:
1
The first period of the periodic table consists only of Hydrogen and Helium. Both of these elements exist in the gaseous state under standard temperature and pressure conditions, making it the only period composed entirely of gases.
88
According to Mendeleev's Periodic Law, how were elements arranged in his periodic table?
Answer:
increasing atomic masses
Dmitri Mendeleev formulated his periodic law based on the observation 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 of undiscovered elements.
89
In which year did John Newlands propose the Law of Octaves, stating that elements arranged by increasing atomic mass exhibit repeating properties every eighth element?
Answer:
1864
John Newlands proposed his Law of Octaves in 1864. He observed that when elements are arranged in order of increasing atomic mass, the physical and chemical properties of every eighth element are similar to those of the first, analogous to musical octaves. This was a significant early attempt at classifying elements based on periodicity, though it was only fully applicable to lighter elements up to calcium.
90
Who is credited with the development of the modern periodic table based on atomic number?
Answer:
Mosley
Henry Moseley established the modern periodic law by demonstrating that the properties of elements are a periodic function of their atomic number, rather than atomic mass, which was the basis for earlier tables.