Railway Science (Chemistry-Structure of Atom) (Part-II)

Total Questions: 50

21. Which of the following is not a heteroatomic molecule ? [RRB Group D 16/11/2018 (Morning)]

Correct Answer: (c) P₄
Solution:

The atomicity of Phosphorus is Tetra-atomic. A heteroatomic molecule is a molecule that contains more than one type of atom. . Heteroatomic molecules can also be polyatomic, meaning they consist of more than three atoms of different elements. Example - CO2, CH₄ , NH₃ .

22. Which of the following is monoatomic? [RRB Group D 4/12/2018 (Afternoon)]

Correct Answer: (b) Argon
Solution:

It is a chemical element with the symbol Ar and atomic number 18. It is placed in group 18 of the periodic table and is a noble gas. Monatomic: Molecule composed of just one atom, and lacking any covalent bonds. The noble gasses Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn), are all monatomic.

23. ______ is a fourth-atomic element. [RRB Group D 05/12/2018 (Evening)]

Correct Answer: (d) phosphorus
Solution:

The number of atoms present in the molecule of an element is known as its Atomicity. Atomicity of other elements: Argon (Ar) - 1, Copper (Cu) - 1, Chlorine (Cl) - 2.

24. A ____ can be defined as a part of a _____ or a _______ fraction of a compound that is capable of independent existence and shows all the properties of that element. [RRB Group D 13/12/2018 (Afternoon)]

Correct Answer: (a) Molecule, element, smallest
Solution:

A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. Molecules of many elements, such as Argon (Ar), Helium (He) etc. are made up of only one atom.

25. If the atomic number of Krypton is 36, then its electronic configuration is: [RRB ALP Tier - I (09/08/2018) Afternoon]

Correct Answer: (c) 2, 8, 18, 8
Solution:

Krypton (Kr) - It belongs to group 18 (noble gas) elements. Electronic configuration - The arrangement of electrons in orbitals around an atomic nucleus. Krypton is used commercially as a filling gas for energy-saving fluorescent lights.

26. Except Helium, all noble gasses have how many electrons in the outermost shell? [RRB ALP Tier - I (10/08/2018) Morning]

Correct Answer: (c) 8
Solution:

Helium has 2 electrons in its outermost shell. Other noble gasses are neon (10), argon (18), krypton (36), xenon (54) and radon (86). All noble gasses have 8 electrons in their valence, that is, they have completely filled octets. Fully filled octets stabilize these elements and thus their valencies are zero (0). All other elements form cations and anions to achieve a noble gas-like stable configuration.

27. Which one of the following elements has the lowest atomic mass? [RRB ALP Tier - I (10/08/2018) Evening]

Correct Answer: (d) Hydrogen
Solution:

The first element in the Periodic Table. Atomic Mass is the sum of the number of protons and neutrons present in the atom of the element. The elements are arranged in the periodic table in the increasing order of their atomic masses. Helium (He) (Atomic number - 2), (Atomic Mass - 4.0026 u). Lithium (Li) (Atomic number - 3), (Atomic Mass - 6.94 u) and Nitrogen (N) (Atomic number - 7), (Atomic Mass - 14.007 u).

28. Which of the following elements has a total of 3 shells with 8 electrons in the last orbit ? [RRB ALP Tier - I (20/08/2018) Morning]

Correct Answer: (b) Ar
Solution:

Valency of an element is a measure of its combining power with other atoms in a chemical compound. Atomic number - 18, Atomic Mass - 39.95 u. The inert gas, Argon (Ar) is the third most abundant gas (0.93%) in the atmosphere. Other elements and their atomic number : Al (Aluminium) - 13, P (phosphorus) - 15, S (Sulphur) - 16.

29. An element has an atomic weight of W and an atomic number of N. The number of protons in the nucleus of its atom is: [RRB ALP Tier - I (20/08/2018) Morning]

Correct Answer: (c) N
Solution:

Atomic weight - The total weight of an atom which is equal to the number of protons and neutrons. Atomic Number - The number of protons in the nucleus of an atom.

30. The number of valence electrons in an atom of Phosphorus is: [RRB ALP Tier - I (21/08/2018) Morning]

Correct Answer: (d) 5
Solution:

Phosphorus (P): Atomic number (15). Properties : Non-metal, Neutral element (number of protons and electrons are equal). Uses: In the production of fertilizers. Red phosphorus used in the production of safety matches. Valence electrons are the electrons in the outermost shell or energy level of an atom. Example - Oxygen's valence electrons (6) as 2s², 2p⁴. Phosphorus outermost orbitals as 3s² 3p³ .