Final answer:
PH3, also known as phosphine, is a polar molecule due to its trigonal pyramidal molecular geometry and the uneven distribution of charge caused by the lone pair of electrons on the phosphorus atom.
Step-by-step explanation:
The molecule PH3, known as phosphine, is indeed polar. Phosphine's molecular geometry is trigonal pyramidal, similar to NH3 (ammonia), which is a classic example of a polar molecule. Each hydrogen in PH3 has a slight positive charge due to phosphorus being more electronegative, and the lone pair of electrons on phosphorus contributes to the molecule's asymmetry. This asymmetrical shape leads to an uneven distribution of charge, making the molecule polar. Just as in NH3, the lone pair on the central atom of PH3 is not balanced by another atom directly opposite to it, contributing to the overall polarity of the molecule. As a result, the molecule has a net dipole moment, where the negative end of the dipole is at the phosphorus atom, and the positive end is distributed among the three hydrogen atoms.