The interest of the government bond is calculated and paid quarterly. To establish what the quarterly interest rate is, you divide the interest rate of 4% by 4, which is 1.0%. This is paid each quarter and is not reinvested in the bond.
Quarter 1 100,000 x 1.0% = $1,000
Quarter 2 100,000 x 1.0% = $1,000
Quarter 3 100,000 x 1.0% = $1,000
Quarter 4 100,000 x 1.0% = $1,000
Total Interest $4,000
The total return is $4,000 in interest on your $100,000.
To express this as a percentage it is $4,000 divided by $100,000. The return for the government bond is 4% (0.04).