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

Total Questions: 50

11. The elements present in any one group have the same _________ . [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (b) number of valence electrons
Solution:

Valence electron is an outer shell electron with an atom. These electrons participate in the formation of a chemical bond. Number of valence electrons decides whether an element is electronegative or electropositive in nature. For example, Oxygen has six valence electrons, two in the 2s subshell and four in the 2p subshell.

12. "When elements are arranged in the order of increasing atomic masses, the properties of the first element is similar to those of the eighth element like with musical notes’__ this law is known as: [RRB Group D 19/09/2018 (Evening)]

Correct Answer: (c) Newlands law of octaves
Solution:

In 1866, John Newlands, an English scientist, arranged the then known elements in the order of increasing atomic masses. He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element. He found that every eighth element has properties similar to that of the first.

13. The valency of nitrogen in ammonia is: [RRB Group D 19/09/2018 (Evening)]

Correct Answer: (b) 3
Solution:

In ammonia which is NH₃, one atom of nitrogen combines with 3 atoms of hydrogen. The valency of nitrogen is 3 because it needs 3 atoms of hydrogen to form ammonia.

14. The element present in the fourth period and in the second group is _________ . [RRB Group D 20/09/2018 (Afternoon)]

Correct Answer: (a) Calcium
Solution:

Other Elements - Potassium (K) - First group and fourth period, Scandium (Sc) - Third group and fourth period, Magnesium (Mg) - Second group and Third period, Iron (Fe) - eighth group and fourth period, Nickel (Ni) - tenth group and fourth period.

15. Dobereiner could identify only __________ triads from the elements known at that time. [RRB Group D 20/09/2018 (Afternoon)]

Correct Answer: (b) 3
Solution:

Dobereiner’s law of triads states that when elements are arranged in the order of increasing atomic masses, the atomic mass of the middle element of the triad is approximately the average of the atomic masses of the other two elements. Example - lithium (7), sodium (23), and potassium (39) form a Dobereiner's triad.

16. How many elements were known when Mendeleev started his work? [RRB Group D 20/09/2018 (Evening)]

Correct Answer: (b) 63
Solution:

Mendeleev : Published his first version of the periodic table in 1869. The periodic table of Mendeleev is based on atomic mass. Mendelevium (Md), atomic number (101), is named in honor of Dmitri Mendeleev.

17. The element with atomic number 57 is related to – [RRB Group D 22/09/2018 (Morning)]

Correct Answer: (a) d-block
Solution:

Lanthanum (La) has the atomic number 57; it is classified as lanthanide. The d-block of the periodic table contains the elements of the groups 3-12 in which the d orbitals are progressively filled in each of the four long periods. d-block elements are also known as transition metals.

18. _______ elements are present in the sixth period of the modern periodic table. [RRB Group D 22/09/2018 (Afternoon)]

Correct Answer: (a) 32
Solution:

Sixth period begins with Cesium and ends with Radon. The modern periodic table contains Seven horizontal rows called periods 1 to 7 and Eighteen vertical columns called groups 1 to 18. Elements with respective periods: First period - 2 elements, second period and third periods - 8 elements, fourth and fifth periods - 18 elements, Sixth and seventh period - 32 elements. Q.815. In M

19. In Mendeleev's periodic table, the vertical columns are called: [RRB Group D 22/09/2018 (Afternoon)]

Correct Answer: (c) Groups
Solution:

The horizontal rows are called Periods. Mendeleev’s Periodic Law (in 1869) - The properties of the elements are a periodic function of their atomic weights. Mendeleev’s Periodic table has eighteen groups and seven periods.

20. An element has an atomic number of 20 with which of the following elements will it show similar chemical properties. [RRB Group D 22/09/2018 (Evening)]

Correct Answer: (a) Be(4)
Solution:

Be (4) : Beryllium is the lightest element of the alkaline-earth metals of Group 2. The element having atomic number 20 is Calcium (Ca). Be and Ca show the same chemical properties because these elements belong to the same group II and also have two electrons in their outermost shell. Elements in group 2 - Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).