Hint: In the above question, it is asked how many single covalent bonds can halogens form. The number of covalent bonds depends upon the number of unpaired valence electrons present in the molecule.
Complete step by step solution
Halogens are the Group 17 elements. They have 7 electrons in their valence shell. They need only one electron to completely fill its valence shell and hence, it can form only one single covalent bond.
Additional Information
Atomic orbitals (except for s orbitals) have specific directional properties which decide the type of covalent bonds the compound can form. Sigma ( $ \sigma $ ) bonds are the strongest covalent bonds present due to head-on overlapping of orbitals on two different atoms. When a compound has a single bond then it usually denotes a $ \sigma $ bond. Pi ( $\pi$ ) bonds are weaker and are due to lateral overlap between p or d orbitals. A double bond between any two atoms consists of one sigma and one pi bond, whereas a triple bond consists of one sigma and two pi bonds.
Covalent bonds are also affected by the electronegativity of the connected atoms which determines the chemical polarity of the bond. Two atoms with equal electronegativity will make nonpolar covalent bonds such as H–H. An unequal relationship creates a polar covalent bond such as with H−Cl. Here the electronegativity of chlorine is much more than that of hydrogen.
Note
Certain molecules such as xenon difluoride and sulphur hexafluoride show exceptions as they covalently bond with compounds more than the one which can be predicted by covalent bonding according to the octet rule.
