What was the Bell of arms in the British army?

It was a storeroom in which weapons were kept.

The correct answer is Option 2 - It was a storeroom in which weapons were kept.

The Bell of arms was a storeroom in which weapons were kept.

How the mutinies began in 1857:

The sepoys began their action with a signal:
In many places it was the firing of the evening gun or the sounding of the bugle.
They first seized the bell of arms and plundered the treasury.
They then attacked government buildings – the jail, treasury, telegraph office, record room, bungalows – burning all records.

Late in the afternoon of 10 May 1857, the sepoys in the cantonment of Meerut broke out in mutiny. It began in the lines of the native infantry, spread very swiftly to the cavalry and then to the city. The ordinary people of the town and surrounding villages joined the sepoys. The sepoys captured the bell of arms where the arms and ammunition were kept and proceeded to attack white people, and to ransack and burn their bungalows and property. Government buildings – the record office, jail, court, post office, treasury, etc. – were destroyed and plundered. The telegraph line to Delhi was cut. As darkness descended, a group of sepoys rode off towards Delhi.