The number of non-polar molecules from the following is _________. $$\mathrm{HF}, \mathrm{H}_2 \mathrm{O}, \mathrm{SO}_2, \mathrm{H}_2, \mathrm{CO}_2, \mathrm{CH}_4, \mathrm{NH}_3, \mathrm{HCl}, \mathrm{CHCl}_3, \mathrm{BF}_3$$

<p>To determine whether a molecule is polar or non-polar, we must consider the difference in electronegativity between the atoms and the symmetry of the molecule. Polar molecules occur when there is an electronegativity difference between the bonded atoms. Non-polar molecules either do not have any polar bonds or the polarities cancel each other out because of a symmetrical arrangement. Let's consider each molecule individually:</p> <ul> <li><b>HF</b> (Hydrogen fluoride): This molecule is polar due to the high electronegativity difference between hydrogen (H) and fluorine (F).</li> <li><b>H₂O</b> (Water): It is polar because of its bent shape and the difference in electronegativity between oxygen and hydrogen.</li> <li><b>SO₂</b> (Sulfur dioxide): The molecule is non-linear and has polar bonds, making it a polar molecule.</li> <li><b>H₂</b> (Hydrogen): This molecule is non-polar because it consists of two identical atoms which share electrons evenly.</li> <li><b>CO₂</b> (Carbon dioxide): Even though C=O bonds are polar, the molecule is linear and the polarities cancel out, making CO₂ non-polar.</li> <li><b>CH₄</b> (Methane): It is non-polar because the C-H bonds are evenly distributed in a tetrahedral shape, canceling out any dipole moments.</li> <li><b>NH₃</b> (Ammonia): This molecule is polar; it has a trigonal pyramidal shape with a lone pair on nitrogen, creating a dipole moment.</li> <li><b>HCl</b> (Hydrogen chloride): The molecule is polar due to the electronegativity difference between hydrogen and chlorine.</li> <li><b>CHCl₃</b> (Chloroform): It has polar C-Cl bonds and is not symmetrical, resulting in a polar molecule.</li> <li><b>BF₃</b> (Boron trifluoride): This molecule is non-polar despite having polar bonds, because the shape of the molecule is trigonal planar and the dipoles cancel out.</li> </ul> <p>Given this information, the non-polar molecules from the list are: $\mathrm{H}_2, \mathrm{CO}_2, \mathrm{CH}_4, \mathrm{BF}_3$.</p> <p>Therefore, there are 4 non-polar molecules in the list given.</p>