Railway Science (Chemistry-Periodic Table) (Part-V)

Total Questions: 50

21. In the Modern Periodic Table, which period contains 32 elements ? [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (a) Period 6
Solution:

Period 6 is the longest period in the table, containing 32 elements from Cesium (Cs, atomic number 55) to Radon (Rn, atomic number 86). Period 3, 4, and 5 each contain only 8 elements.

22. The given symbol represents ______ element. [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (b) Hydrogen
Solution:

Hydrogen (H) - the lightest element. At standard conditions hydrogen is a gas of diatomic (H2). It is colorless, odorless, tasteless, non-toxic, and highly combustible.
Carbon (C) : It is nonmetallic and tetravalent. Atomic number - 6. Group - 14. Gold (Au) : Atomic number - 79. Block - d block. Mercury (Hg) : Liquid at room temperature. Atomic number - 80.

23. An element placed in the periodic table with an electronic configuration of 2, 8, 8, 2 belongs to period ________ in the modern periodic table. [RRB Group D 03/10/2018 (Evening)]

Correct Answer: (b) 4
Solution:

The element with electronic configuration 2, 8, 8, 2 is calcium. It belongs to the 2ⁿᵈ  group in the modern periodic table.

24. In Mendeleev's periodic table, _______ appears before nickel. [RRB Group D 04/10/2018 (Morning)]

Correct Answer: (c) Co
Solution:

Mendeleev's periodic table, Cobalt (Co) appears before Nickel (Ni), even though Cobalt has a slightly higher atomic mass than Nickel (58.93 amu vs. 58.71 amu). This was because Mendeleev prioritized chemical and physical properties over strict atomic mass order when arranging elements.

25. Which of the following inert gases is placed in period 5? [RRB Group D 04/10/2018 (Morning)]

Correct Answer: (c) Xe
Solution:

The noble gases, also known as inert gases, are indeed found in Group 18 of the Periodic Table. The noble gases include Helium (He₂), Neon (Ne₁₀), Argon (Ar₁₈), Krypton (Kr₃₆), Xenon (Xe₅₄), and Radon (Rn₈₆).

26. In the modern periodic table, there are two metalloids in each of the ____ and _______ periods. [RRB Group D 04/10/2018 (Afternoon)]

Correct Answer: (d) 4,5
Solution:

Metalloids are the elements with properties of both metals and nonmetals. The metalloids elements in period 4 - Germanium (Ge) and Arsenic (As). The metalloids in Period 5 - Antimony (Sb) and Tellurium (Te). There are Seven metalloids in the modern periodic table.

27. ______ is the last metal in the modern periodic table. [RRB Group D 05/10/2018 (Morning)]

Correct Answer: (b) Polonium
Solution:

Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium.
Metalloids in periodic table with their atomic number: Boron (B) - 5, Silicon (Si) - 14, Germanium (Ge) - 32, Arsenic (As) - 33, Antimony (Sb) - 51, Tellurium (Te) - 52.

28. ________ was discovered later and replaced eka-silicon. [RRB Group D 05/10/2018 (Morning)]

Correct Answer: (c) Germanium
Solution:

Eka-silicon is the placeholder name for an element that was predicted to exist by Dmitri Mendeleev in 1871. He named it eka-silicon because it was predicted to have properties similar to silicon.
Germanium was discovered in 1886 and has properties that are very similar to silicon. Eka-boron - Scandium (Sc). Eka-aluminium - Gallium (Ga).

29. In the modern periodic table, Silicon (Z = 14) is placed between ________ and ________ . [RRB Group D 05/10/2018 (Afternoon)]

Correct Answer: (b) AI & P
Solution:

Silicon: It is placed at the 3rd Period and 14th Group number. Electron configuration - [Ne] 3s² 3p². Aluminum (Al) has an atomic number 13 and Electron configuration- [Ne] 3s² 3p¹ . Phosphorus (P) has an atomic number 15 and Electron configuration- [Ne] 3s² 3p³ .

30. Radioactive elements are placed in ______. [RRB Group D 09/10/2018 (Morning)]

Correct Answer: (a) Actinoides
Solution:

Actinoides is a series of 15 consecutive chemical elements in the periodic table from Actinium (Ac) to Lawrencium (Lr). From atomic numbers 89 -103. These elements are radioactive and have a wide range of oxidation numbers. Radioactivity - Discovered by Henry Becquerel. Lanthanides are a series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57-71 (lanthanum to lutetium).