The reduced vapor pressure at high altitudes causes a liquid to boil at a temperature.
a. lower
b. higher

            Lower Temperature

                        The boiling point is defined as the temperature at which the vapor pressure of a given liquid becomes equal to the external pressure or atmospheric pressure. Boiling point is mainly effected by following factors:

1) Inter-Molecular Interactions:

                                                     Greater the intermolecular interactions greater will be the boiling point because more energy is required to overcome these intermolecular interactions.

Example:

                                          Water  =  100 °C

                              Diethyl ether  =  34.5 °C

Water requires more energy because it contains hydrogen bond interactions which are considered the strongest intermolecular interactions. While, Diethyl ether lacks Hydrogen bondings.

2) External Pressure:

                                    The boiling point also varies with changing the external pressure for the same solvent. Greater the external pressure greater will be the boiling points and vice versa.

Example:

Water:

                    External Pressure                       Boiling Point

                                1 atm                                         100 °C

                             0.921 atm                                     98 °C

                             0.425 atm                                     72 °C

8

explanation:

each principal energy level above the first contains one s orbital and three p orbitals. a set of three p orbitals, called the p sublevel, can hold a maximum of six electrons. therefore, the second level can contain a maximum of eight electrons - that is, two in the s orbital and 6 in the three p orbitals.

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