Which one is correct?
1-The name of all the continents end with the same letter that they start with.
2-The name of all the continents ends with the same letter that they start with.
3-The names of all the continents end with the same letter that they start with.
Number 3 is correct.
Number 1 is right in saying "continents", which is plural, because there is more than one continent. However, it says "name", which is singular, but the continents do not share the same name.
Number 2 is overall incorrect for the same reason, "name" is singular when it should be plural. Also, "ends" is plural, but it should be singular because there is only one end to each name.
Number 3 is correct because there is more than one name for the continents and "names" is plural. Also, "end" is correct because it is singular and each word only has one end.