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

Total Questions: 50

41. In the modern periodic table, elements with atomic numbers 19 to 36 are placed in which period? [RRB Group D 26/09/2018 (Afternoon)]

Correct Answer: (d) 4
Solution:

Elements having atomic numbers 55 to 86 are placed in the Period 6. Elements having atomic numbers 37 to 54 are placed in the Period 5. Elements having atomic numbers 11 to 18 are placed in the Period 3.

42. What are the special characteristics of the following group of elements? [RRB Group D 26/09/2018 (Evening)]

1. All these elements are metals
2. All these elements react with water to form hydrogen gas
3. All these elements have a valency 1

Correct Answer: (b) alkali metal group
Solution:

Alkaline-earth metals : They have two electrons in their outermost shell and are the second most reactive after alkali metals. The halogens : They are highly electronegative and reactive, requiring one electron to complete their outermost shell. Hence, they typically exhibit a -1 oxidation state. They form salts with metals.

43. _____ elements have the largest atoms. [RRB Group D 27/09/2018 (Morning)]

Correct Answer: (d) Li
Solution:

Li - Atomic number - 3, Group First (alkali), Period - second. Lithium is the lightest metal. Largest atom is defined by its atomic radius i.e. the distance between the nucleus to its outermost orbit/ valence shell.
As we move from left to right in the Modern periodic table the atomic radius decreases. But as we go down the period in the Modern periodic table the atomic radius increases.

44. ____ is the property of attracting electrons by the halogen atoms in a molecule. [RRB Group D 27/09/2018 (Morning)]

Correct Answer: (d) Electronegativity
Solution:

Electronegativity - A measure of the tendency of an atom to attract a bonding pair of electrons. Fluorine (F) with atomic number 9 is the most electronegative element.
Electron affinity - A change in the energy of a neutral atom when an electron is added to it.
Electrochemistry - the study of the relationship between electricity and chemical reactions. Electropositivity - A tendency of an atom to donate an electron.

45. Which of the following inert gases is placed in period 4 of the periodic table? [RRB Group D 27/09/2018 (Morning)]

Correct Answer: (a) Kr
Solution:

Krypton (Kr): Atomic number - 36 : Inert gases: Belong to Group 18 of the Periodic Table. Inert gases: Helium (He) - Period (1), Atomic number - 2. Neon (Ne) - period 2, Atomic number - 10. Argon (Ar) - Period 3, Atomic number - 18. Xenon (Xe) - Period (5), Atomic number - 54. Radon (Rn) - Period (6), Atomic number - 86.

46. _____ is the first metalloid in the modern periodic table. [RRB Group D 27/09/2018 (Afternoon)]

Correct Answer: (b) B
Solution:

Metalloids have properties of both metals and nonmetals. Metalloids belong to p-block elements and they are placed on the right side of the periodic table. There are seven metalloids in the modern periodic table included - Boron, Silicon (Si), Germanium (Ge), Arsenic (As), Tellurium (Te), Antimony (Sb), Polonium (Po).

47. The valency of Mercurous ion is: [RRB Group D 27/09/2018 (Afternoon)]

Correct Answer: (a) 1
Solution:

Mercury (Hg) forms Mercurous and Mercuric compounds with 1 and 2 valencies respectively. Mercury has the least electron affinity. The atomic number of Mercury is 80. Mercury is also called quicksilver.

48. _____ metal melts on our palm. [RRB Group D 27/09/2018 (Evening)]

Correct Answer: (c) Gallium
Solution:

Gallium (Ga - Atomic number 31). Cesium is also a metal that melts on our palm. They have a very low melting point and only the heat from our palm is enough to easily melt.Potassium (K - 19) - Alkali metal, Floats in water, a soft and shiny metal.
Magnesium (Mg - 12) : Isolated by - Sir Humphry Davy. Aluminum (Al - 13) : Discovered by Hans Christian Oersted, third most abundant element in the Earth’s crust, capable of superconductivity.

49. The maximum number of electrons in the third shell is ______. [RRB Group D 27/09/2018 (Evening)]

Correct Answer: (a) 18
Solution:

Electronic configuration - Way of distribution of electrons in atomic orbitals. The number of electrons accommodated in the shell is represented by the principal quantum number ‘n’, where the total number of an electron in the shell (energy shell) is given by the formula 2n² , n = Shell number. The electrons can be distributed in the K (2), L (8), M (18), N (32) based electron shell.

50. Atomic number of N is 7, then the atomic number of the third element of the nitrogen family is: [RRB Group D 27/09/2018 (Evening)]

Correct Answer: (b) 33
Solution:

Group 15 (Nitrogen family) - Nitrogen (N), Phosphorus (P - 15), Arsenic (As - 33), Antimony (Sb - 51) and Bismuth (Bi - 83), Moscovium (Mc - 115). The p-block elements are placed on the right side of the main periodic table.
Oxygen family (chalcogens) - Elements belong to group 16 elements : Oxygen (O - 8), Sulfur (S - 16), Selenium (Se - 34), Tellurium (Te - 52), and Polonium (Po - 84), Livermorium (Lv - 116).