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

"the periodic table is arranged in order of atomic number."

b. accuracy of the data matters alot more than its number of digits, organization or amount of detail. quantitative observation is more accepted than the qualitative observation.