Which Australian regulatory authority would handle issues relating to securities and market practices?

The Australian Securities and Investments Commission (ASIC) is the correct answer because it is the primary regulatory body responsible for overseeing and enforcing laws pertaining to companies, securities, and financial services within Australia. ASIC regulates the Australian financial markets and plays a critical role in protecting consumers and investors by ensuring that companies and financial institutions adhere to the legal standards established to maintain market integrity and transparency.

The other regulatory bodies mentioned serve different purposes; for example, the Australian Taxation Office (ATO) manages tax collection and enforcement of tax laws, but it does not oversee securities or market practices. The Monetary Authority of Singapore (MAS) is the financial regulatory authority in Singapore, not Australia, which makes it unrelated to this question. The Foreign Investment Review Board (FIRB) examines foreign investment proposals to determine if they are in the national interest, but it does not focus specifically on securities or market practices. Thus, the role of ASIC in monitoring and regulating securities aligns perfectly with the inquiry about handling securities and market issues in Australia.