Answer: A) hydrogen
Explanation: Covalent bonds are formed by sharing of electrons whereas ionic bonds are formed by transfer of electrons.
Hydrogen is an element with atomic number of 1 and thus contain 1 electron.
\(H:1:1s^1\)
It can only share electrons to attain stable configuration as on losing the electron it wont exist.
Lithium is an element with atomic number of 3 and thus contain 3 electrons.
\(Li:3:1s^22s^1\)
It can lose 1 electron to attain stable configuration.
Potassium is an element with atomic number of 19 and thus contain 19 electrons.
\(K:19:1s^22s^22p^63s^23p^64s^1\)
It can lose 1 electron to attain stable configuration.
Sodium is an element with atomic number of 11 and thus contain 11 electrons.
\(Na:11:1s^22s^22p^63s^1\)
It can lose 1 electron to attain stable configuration.
