Answer:
a. a dipole.
Explanation:
A dipole -
The term Dipole , can be bifurcated as di + pole , i.e. , two poles .
Hence, any species or compound where two poles i.e. , a positive and a negative is possible , is termed to as a dipole .
For example , in water molecule ,
The more electronegative atom , i.e. , oxygen attains a negative charge and correspondingly , the hydrogen atom have a positive charge , and hence can give rise to a dipole .