Assertion (A) : In the periodic table of chemical elements, electron affinity is always found to increase from top to bottom in a group.
Reason (R) : In a group, the atomic radii generally increase from top to bottom.
(a) Both
(A) and (R) are individually true, and (R) is the correct explanation of
(A).
(b) Both
(A) and (R) are individually true, but R is not the correct explanation of
(A).
Correct Answer:
(D)
is false but (R) is true.
In the periodic table of chemical elements, the electron affinity decreases down the group but increases up for the group and from left to right across periods of a periodic table because the electron added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons. An atom gets larger as the number of electronic shells increases. Therefore, the radius of atoms increases as you go down a certain group in the periodic table of elements. However, the size of an atom will decrease as you move from left to right of a certain period. Thus, Assertion (A) is false, while Reason (R) is true.
Ques: 2
Which of the following is a fundamental element :
Correct Answer:
(B) Diamond
Chemically diamond is the purest form of Carbon (crystal structure). Hence, it is a fundamental element. Sand is basically made up of Silicon and Oxygen, Marble is made up of Calcium, Carbon and Oxygen while sugar is mainly the compound of Carbon, Hydrogen and Oxygen.
Ques: 3
Which of the following is the most common element in the Universe?
Correct Answer:
(A) Hydrogen
The most abundant element in the Universe is Hydrogen, which makes up about 3/4 of all matter. Helium makes up most of the remaining 1/4. Thus, it is clear that hydrogen is the most common and abundant element in the Universe. While the most abundant element in the earth's crust is Oxygen making up 46.6% of earth crust.
Ques: 4
Which is the most abundant element after Oxygen?
Correct Answer:
(A) Silicon
The most abundant element on earth's surface after Oxygen is Silicon. It was discovered by J.J. Berzelius in 1824. The word 'Silicon' was taken from the Latin word silex. Silicon chips are used as a semiconductor in computers.
Ques: 5
The element found maximum in the soil layer is –
Correct Answer:
(A) Oxygen
The element found the maximum in the soil layer is Oxygen 46.60% followed by Silicon 27.72%, Aluminium 8.13%, Iron 5.00% and Calcium 3.65%.
Ques: 6
What is the usual property of oxides of Group 3 and 4?
Correct Answer:
(A) Basic and Acidic
The usual property of oxides of Group 3 and 4 of the periodic table are basic and acidic. These oxides are amphoteric (able to react both as a base and as an acid).
Ques: 7
Consider the following statements with reference to the periodic table of chemical elements :
1. Ionization potential gradually decreases along a period
2. In a group of elements, electron affinity decreases as the atomic weight increases
3. In a given period, electronegativity decreases as the atomic number increases
Which of these statement (s) is/are correct ?
Correct Answer:
(B) 2 only
The ionization energies are dependent upon the atomic radius. Since going from left to right across a period in the periodic table, the atomic radius decreases and the ionization potential increases while ionization potential decreases as one moves down a given group. In a group of elements, from top to bottom the electron affinity decreases as the atomic weight increases. As one moves trend- wise from left to right across a period in the periodic table, the electro-negativity increases due to the stronger attraction that the atoms obtain as the nuclear charge increases.