Nicodemus

What is meant by Nicodemus “being one of them” (John 7:50)?
He is one of “the rulers - i.e., a member of the Sanhedrin, the ruling council of Israel - [and] the Pharisees” (John 7:48).

When did Nicodemus come to Jesus “by night” (John 7:50)?
Early in Jesus' ministry, as recorded in John 3.

How did his conversation with Jesus that night go?
It went over Nicodemus' head: see Born Again, How Can These Things Be, Bronze Snake, and John 3:16 Meaning.

What had Nicodemus been up to since that conversation with Jesus?
He must have mulled over what Jesus taught him and at least kept up with news about Jesus. It is also possible, if not probable, that Nicodemus had been in at least some of the the crowds that Jesus has taught since that night, especially in Jerusalem. And since the crucified body of Jesus was buried by Nicodemus and another member of the Sanhedrin (see Joseph of Arimathea), it is even possible that Nicodemus had been witnessing about Jesus to his friends in the Sanhedrin.

What does Nicodemus do in John 7:51?
He stands up for Jesus by reminding them of the Jewish law that forbids condemning any accused person until they have had a chance to speak for and defend themselves.

Do they appreciate his reminder?
The sophisticated Jerusalemites disdained the provincial backwaters of Galilee. “Are you also from Galilee?” (John 7:52) was a derision to an Jerusalemite, and an insult to a member of their esteemed Sanhedrin.

Was it true that “no prophet has arisen out of Galilee” (John 7:52)?
2 Kings 14:25 identifies Jonah as “the prophet from Gath Hepher,” which was a town in the land that God gave to the tribe of Zebulun in Galilee. The prophets Nahum and Hosea were also born in the north, although whether or not they were born in Galilee is unclear. So at least one prophet had arisen out of Galilee.

Then why did they claim that “no prophet has arisen out of Galilee” (John 7:52)?
They were angry and lashing out to have the last word before disbanding: “And everyone went to their own house” (John 7:53).

Based on John 7:50-52, what is the correct answer to the question in John 7:48: “Have any of the rulers or of the Pharisees believed in Him?”
Yes, at least one of them - Nicodemus - believed in Jesus at this point.