Which is most likely true about electronegativity?

a. it tends to be the same across a periodb. it tends to be the same down a groupc. it tends to increase across a period

d. it tends to increase down a group?

Electronegativity is the tendency of an element to attract the bonded electrons towards itself. In a group, as the atomic radius increases electronegativity decreases as the outermost electron is far away from the nuclear attraction. In a period, the atomic size decreases. So, the effective nuclear charge experienced by the outermost shell increases. Therefore, across a period the electronegativity increases as the increased effective nuclear charge leads to the attraction of bonded electrons with greater ease.

Therefore the correct answer is c, electronegativity tends to increases across a period.