In addition to the second question
If governments print money to pay off the national debt, inflation would rise. This increase in inflation would reduce the value of government bonds.
If inflation increases, people will not want to hold bonds because their value is falling. Therefore, the government will find it difficult to sell bonds to finance the national debt. They will have to pay higher interest rates to attract investors.
If the government print too much money and inflation get out of hand, investors will not trust the government and it will be hard for the government to borrow anything at all.
Therefore, printing money could create more problems than it solves