In ammonia, a central nitrogen atom is bonded to three hydrogen atoms. similarly, boron trifluoride has a central boron atom bonded to three fluorine atoms. however, ammonia is pyramidal and boron trifluoride is trigonal planar in shape. which statement justifies this difference in their structure?

The lone pair of electrons on the nitrogen in ammonia decreases the bond angle between the bonding pairs, giving it a pyramidal structure. 

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.

There is one s orbital, and there are three p orbitals, five d orbitals, and seven f orbitals. thus, the answer is b. do not confuse the number of orbitals in a subshell with the number of electrons the subshell can hold. each orbital can hold two electrons, so the capacity of an nf subshell is 14 electrons.