The answer is complicated to be honest. There are no assets that are completely risk free. However, there are a lot of assets that are almost risk free. For example, what are the chances that the US will go bankrupt tomorrow? I don’t think that is a realistic scenario so the debt that the US issues can be considered a risk free asset. There are more countries that are in the same good shape as the US such as the UK, Germany,Canada, Australia etc. The bonds that these countries issue can be considered as risk free.