#2 is true, but extremely unlikely.
Risk-free basically means the lowest possible risk. Not true zero risk.
not really, with private bonds it's replaced with the risk of the company defaulting or declaring bankruptcy.
This risk is likely also going to be true for the Dollar, so bonds don't carry any more risk than USD in this regard.
> This risk is likely also going to be true for the Dollar
It can't be, because it doesn't apply to the currency, which while it is structurally created by creation of debt is not a debt the government is obligated to pay and on which it can fail and default.
> so bonds don't carry any more risk than USD in this regard
Even if there was a default risk in the dollar, bonds necessarily have more risk since they are fully exposed to every risk to the currency they are denominated in and also their own default risk, which even if the currency had such a risk would sit on top of it.
Although Brexit happened, so never say never I guess
They may be called that, but they aren't. There are at least two risks associated with U.S. government bonds:
1. Inflation can exceed the interest rate on the bond and cause it to lose value when measured in actual purchasing power
2. Political dysfunction could cause the U.S. government to default notwithstanding its ability to print money
(To be fair, #1 is a risk associated with any bond. #2 is peculiar to U.S. government bonds.)