At Pentecost, the Holy Spirit descended upon the apostles and other believers, as recorded in Acts 2:1-4. On the day of Pentecost (fifty days after Passover), the disciples were gathered together in one place in Jerusalem. Suddenly, a sound like a violent rushing wind filled the house, and tongues of fire appeared and rested on each of them. They were all filled with the Holy Spirit and began to speak in other languages (tongues), enabling people from many different nations present in Jerusalem to hear the gospel in their own languages.
This event marks the birth of the Christian Church. Peter then preached a powerful sermon explaining what had happened, quoting the prophet Joel's prophecy about the outpouring of God's Spirit (Joel 2:28-32). About three thousand people believed and were baptised that day (Acts 2:41).
The other options describe separate events. Paul's conversion occurred later, on the road to Damascus (Acts 9). Jesus' ascension took place ten days before Pentecost, forty days after His resurrection (Acts 1:9). While the disciples were arrested on various occasions throughout Acts, this did not happen at Pentecost itself.