Final answer:
Bitcoin faces challenges such as the potential for tax evasion or fraud, as well as a general lack of understanding about cryptocurrencies.
Step-by-step explanation:
Bitcoin, the most popular cryptocurrency, has been subject to various criticisms and challenges. Some argue that bitcoin is riddled with problems such as the potential for tax evasion or other types of fraud, as well as a general lack of understanding about cryptocurrencies. These concerns stem from bitcoin's decentralized nature, which makes it harder to regulate and monitor transactions. Additionally, the anonymous nature of transactions in bitcoin makes it a target for illegal activities.