How did Suraj know Sunder Singh was at the tunnel?
When Suraj was travelling on the night mail train with his father about a week later, he saw a lamp near the tunnel entrance just as the engine let out a shrill whistle.
Although he couldn't see Sunder Singh in the darkness, the presence of the lamp told Suraj that his friend was there, performing his duty as the watchman.
Explanation
The chapter describes Suraj's train journey: 'Suraj heard the rumble as the train passed over a small bridge. It was too dark to see the hut near the cutting, but he knew they must be approaching the tunnel. He strained his eyes looking out into the night; and then, just as the engine let out a shrill whistle, Suraj saw the lamp. He couldn't see Sunder Singh, but he saw the lamp, and he knew that his friend was out there.'
Solution Steps
Suraj was travelling on the night mail train with his father about a week later
He saw a lamp near the tunnel entrance just as the engine let out a shrill whistle
Although he couldn't see Sunder Singh in the darkness, the lamp's presence indicated his friend was there performing his duty as the watchman