The correct answer is a and b. Explanation & Key Takeaways: Analysis of all the 3 statements: Statement a. HF and H2O are polar molecules • H−F and H-O bonds are polar due to the high electronegativity of fluorine and oxygen respectively. • Hence HF and H_(2)O are polar molecules. • Hence a is correct Statement b. CH4 and CO2 are non-polar molecules • There is a small difference in electronegativity between the Carbon and Hydrogen bonds. • Thus, there is no net (overall) polarity. • That makes CH4 a nonpolar molecule. • CO2 is a linear molecule so the resultant dipole moment is zero • Since the individual dipole moments of CO bond cancel each other. • That makes CO2 a polar molecule. • Hence b is correct Statement c. CO2 and SO2 are non-polar molecules • CO_(2) is a linear molecule, so the resultant dipole moment is zero. • Since the individual dipole moments of CO bond cancel each other. • Whereas, SO_(2 )is an angular molecule due to which it has a net dipole moment. • Therefore SO_(2) is polar and CO_(2) is non-polar. • Hence c is not correct. Important Notes: • Polar Molecules • They produce the strongest force and forms H bonds or dipole-dipole bonds. • Polar molecules interact with other polar substances. • These molecules have positive and negative charges on the opposite ends when the more electronegative atom tries to pull electrons towards itself than the less electronegative atom. • Such bonds are known as a polar covalent molecule or simply polar molecule. • Therefore, they are electrically charged. Example: Sulphur, etc • • Nonpolar Molecules • They produce the weakest force and forms Van Der Waal interactions between nonpolar bonds. • Nonpolar molecules do not interact with other nonpolar substances. • Does not have a large number of charges at opposite ends. • Example: Carbon dioxide, etc.