Question

describe the symmetries of each molecule shown
a. benzene b. water c. hydrogen peroxide

b. describe the symmetries of the water molecule. select the correct choice below and, if necessary, fill in the answer box(es) to complete your choice
a. the water molecule has the following rotational symmetry(ies) \\(\square^\circ\\), point symmetry, and does not have reflectional symmetry
(use a comma to separate answers as needed. do not include the degree symbol in your answer.)
b. the water molecule has \\(\square\\) line(s) of symmetry, point symmetry, and the following rotational symmetry(ies) \\(\square^\circ\\)
(use a comma to separate answers as needed. do not include the degree symbol in your answer.)
c. the water molecule does not have any symmetry

Explanation:

The water molecule (H₂O) has a bent molecular geometry. It has 2 lines of symmetry (one through the O and the midpoint of the H - H bond, and another perpendicular to that, bisecting the H - O - H angle). It has rotational symmetry of 180° (since rotating 180° around an axis through O and perpendicular to the molecular plane maps the molecule onto itself). It also has point symmetry (inversion symmetry) as inverting through the O atom maps H atoms to each other. Option A is wrong as it says no reflectional symmetry, but water has reflectional symmetry (the lines of symmetry). Option C is wrong as water has symmetries. So Option B is correct. The number of lines of symmetry is 2, and rotational symmetry is 180.

Answer:

B. The water molecule has 2 line(s) of symmetry, point symmetry, and the following rotational symmetry(ies) 180°