Question

Which of the following elements is electronegative?
A.Sodium
B.Oxygen
C.Magnesium
D.Calcium

Answer 1

Electronegativity, symbol l$\chi$, measures the tendency of an atom to attract a shared pair of electrons (or electron density). An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons. Using these factors we will answer the question.

Complete answer:
In the periodic table there are many elements. In the periodic table there are many trends. We will see the trend in electronegativity. On moving down the group electronegativity increases and on moving across the period from left to right the electronegativity decreases.
The first option is Sodium. Sodium is present in the first group of the third period.
The next element in the option is oxygen. Oxygen present in group 16 and second period.
In the next option we have magnesium. Magnesium is present in group 2 and second period.
The next element is calcium. Calcium is present in group 2 fourth period.
So when we check the trend, the element in the lower side will be electronegative. So the element in the fourth period is calcium but it is a metal so it is electropositive. The element which is present at the right side of the table will be most electronegative. We have oxygen on the right side of the periodic table.

So, the correct answer is B. Oxygen.

Note:
The trends in the periodic table are very important and should be learnt. Electropositive elements have a tendency to donate electron pairs to become cations whereas electronegative elements have a tendency to accept electron pairs and become anions.