The following three compounds are known to exist.
Choose the most reasonable combining capacity, or valence, for phosphorus.
This is correct. We see that, in all three cases, there are three atoms bonded to the phosphorus. Its valence must be three.
I am sorry, but this is not correct. The valence is the combining capacity. Count the number of atoms connected to the phosphorus.
I am sorry, but this is not correct. Remember that the valence is the combining capacity. Count the atoms connected to phosphorus.
Count the number of atoms connected to phosphorus. This number is the combining capacity, which later came to be called valence.
