Question

(A) : The second electron affinity of oxygen is endothermic.
(R) : Oxygen is the second highest electronegative element.
The correct answer is:
A.Both (A) and (R) are true and (R) is the correct explanation of (A)
B.Both (A) and (R) are true and (R) is not the correct explanation of (A)
C. (A) is true but (R) is false
D. (A) is false but (R) is true

Answer 1

Hint:The energy required to add an electron to the atom is called energy gain enthalpy. When energy is absorbed for addition of electrons, then it is endothermic. Electronegativity is the tendency of an atom to attract a shared pair of electrons towards itself.

Complete answer:
Oxygen is an element which is denoted by the symbol O and it has atomic number eight. Oxygen readily forms oxides with most of the elements and even with most of the compounds.
Electronic configuration of oxygen is 2 in the first orbit and 6 in the second orbit.
So, we can say that oxygen needs more than two electrons to attain stability or to complete its octet state.
When one electron is gained by oxygen it gets a minus one charge on it. When we want to add one more electron to oxygen after addition of one electron then the second electron will face repulsion from other electrons in the valence shell of oxygen. So, to overcome the repulsion by the other atoms of the valence shell we provide heat. Therefore, we can say that addition of a second electron to oxygen is an endothermic reaction. So, the assertion is true.
Oxygen is a small atom and as we read earlier that electronegativity depends upon atomic number and distance between the valence electrons and nucleus, the smaller the distance the greater the electronegativity of the element. As oxygen needs just two electrons to attain octet state it chooses to gain two electrons rather than donate six electrons. So, oxygen being small and has great affinity for electrons it is the second most electronegative element in the periodic table.
Therefore, (A) and (R) are true statements but (R) is not the correct explanation of (A).

Thus, the correct option is B.
Note:
The most electronegative element in the periodic table is Fluorine. It is small and needs just one electron to attain octet state.An atom's electronegativity is affected by its atomic number and the distance from valence electron to the charged nucleus. Smaller atoms with higher number of electrons are most electronegative.