In the context of blockchain technology, answer the following questions: i. What is a digital signature? Assume Bob has created a transaction to send some money to Alice. Why should Bob put his digital signature along with his public key inside the transaction? (6 marks) ii. What is double spending? How it can be detected and prevented in a blockchain? (4 marks) iii. What is the 51% attack? How does it work? (4 marks) iv. Explain how malicious nodes (inside the blockchain's peer-to-peer network) are prevented from tampering with transactions using cryptographic hash functions. Assume each transaction contains the digital signature as well. (4 marks) V. Name and describe TWO applications other than cryptocurrency for blockchain. (2 marks) vi. What does the immutability of the blockchain mean?