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

Total Questions: 50

41. Elements were classified on the basis of their______ [RRC Group D 29/09/2022 (Morning)]

Correct Answer: (b) different physical as well different chemical properties
Solution:

Elements are classified into Metals, Nonmetals and Metalloids on the basis of their different physical and chemical properties. Metals - Electro-positive elements. Examples - Copper, Silver, Iron, Mercury etc.
Non-metals - Electron-negative elements. Examples - Carbon, Sulphur, Bromine, Hydrogen, Nitrogen etc. Metalloids - Both metals and nonmetals. Examples - Boron, Silicon, Arsenic etc.

42. According to Newlands law of octaves, which of the following elements have the same properties? [RRC Group D 29/09/2022 (Afternoon)]

Correct Answer: (a) Be and Mg
Solution:

Every eighth element has similar properties when the elements are arranged in the increasing order of their atomic masses. Classified the known 56 elements into 11 groups based on their similar physical properties. It was applicable only upto calcium.

43. Which of the following elements shows maximum metallic character? [RRC Group D 29/09/2022 (Afternoon)]

Correct Answer: (a) Sc
Solution:

(Scandium). As per Modern Periodic Table, Metallic character increases down the group and decreases across a period. Cesium has the most metallic character and Fluorine has the most nonmetallic character.

44. Which of the following statements with respect to position of elements having atomic number 11, 12, 13, 14, 15, 16, 17 and 18, respectively, in the modern periodic table is INCORRECT? [RRC Group D 30/09/2022 (Morning)]

Correct Answer: (b) These elements belong to the second period of the modern periodic table.
Solution:

The maximum number of electrons that can be filled in the shell K, L, M, N respectively are 2, 8, 18, 32. Atomic number 11 - Sodium (Na), alkali metal, valency - 1. Atomic number 12 - Magnesium (Mg), Alkaline earth metal, valency - 2. Atomic number 13 - Aluminum (Al), valency- 3.
Atomic number 14 - Silicon(Si), valency- 4, Atomic number 15 - Phosphorus(P), valency - 5 or (-3). Atomic number 16 - Sulfur(S), valency - 2. Atomic number 17- Chlorine(Cl), Halogen, valency - 1. Atomic number 18 - Argon(Ar), Noble gas, valency - 0.

45. Select the correct increasing order of atomic radii. [RRC Group D 30/09/2022 (Afternoon)]

Correct Answer: (c) B < Be < Li < Rb
Solution:

On moving down the group, the atomic radius increases. On moving from left to right in a period, the atomic radius decreases.

46. Which of the following metals has least reactivity? [RRC Group D 30/09/2022 (Evening)]

Correct Answer: (d) Gold
Solution:

Atomic Number - 79, Atomic Mass - 196.97u. It is a soft, bright, dense, soft, malleable, and ductile metal with a slightly reddish-yellow colour. Silver (Ag): Atomic Number - 47, Atomic Mass - 107.868 g.mol⁻¹ . It is abundant in mineral-rich soils available generally in crystal form.

47. Why were noble gases NOT included in the Newlands law of octaves? [RRC Group D 30/09/2022 (Evening)]

Correct Answer: (a) These elements were not known at that time.
Solution:

Newland's Law of Octaves: Elements arranged in increasing order of Atomic Mass, the properties of every eighth element starting from any element are a repetition of the properties of the starting element.
Limitations: True only for Elements up to Calcium. Several elements were fit into the same slots. For example - cobalt and nickel. Elements with dissimilar properties were grouped together.
For example - the halogens were grouped with metals such as cobalt, nickel and platinum. Elements that were discovered later could not be fit into the octave pattern.

48. Use Mendeleev's periodic table to select the correct formula for the oxides of Ba and K. [RRC Group D 06/10/2022 (Afternoon)]

Correct Answer: (a) BaO and 𝐾₂0
Solution:

According to Mendeleev's periodic table - Potassium (K) is a metal and it forms a metallic oxide which is basic in nature. The formula for Potassium oxide is Kβ‚‚O. Barium (Ba) belongs to Group- 2 and the formula for its oxide is Barium oxide (BaO).

49. Which among the following elements possesses a greater tendency to gain electrons? [RRC Group D 06/10/2022 (Afternoon)]

Correct Answer: (b) Fluorine
Solution:

Halogens have the highest electron gain enthalpy (electron affinity). Normally electron affinity decreases as we move down the group and increases going left to right across a period because of increased nuclear attraction. Carbon < Nitrogen < Oxygen < Fluorine.

50. Which element is NOT present in the VIII group and first series of the fourth period in Mendeleev's periodic table ? [RRC Group D 06/10/2022 (Evening)]

Correct Answer: (c) Cu
Solution:

Mendeleev's periodic table: According to it, β€œthe properties of elements are the periodic function of their atomic masses.” Merits: Some gaps were left for the elements yet to be discovered.
Demerits: Place of hydrogen was not decided; Due to the irregularity in increase in atomic mass, place of future elements was not certain; Discovery of isotopes violated Mendeleev’s periodic law. There are 18 groups and 118 known elements in the modern periodic table.