Satoshis and Divisibility

How many millisatoshis are in one sat?

• 100
• 1,000
• 100,000,000

A block includes a transaction with a 100-sat output. Is the block valid?

• Yes; dust is a relay rule, so default nodes won't pass such a transaction along, but a block containing it is still valid
• No; any block with a dust output is rejected by every node
• Only if the miner pays a penalty