National debt refers to the total amount of money that a government owes to external creditors, individuals, or institutions. It is a measure of the financial obligations that a country has accumulated over time. However, not all financial instruments or liabilities are considered national debt.

The option 'C', National Saving Certificates, is not viewed as a national debt. Here's why:

1. National Debt:
- National debt typically includes various forms of government borrowings, such as bonds, bills, and loans.
- These borrowings are made by the government to finance its budget deficits or fund public projects and services.
- National debt represents the accumulation of past deficits and is an important indicator of a country's fiscal health.

2. Provident Fund:
- Provident funds are a type of retirement savings scheme implemented by governments or employers.
- They involve regular contributions from employees' salaries, which are invested in various financial instruments to generate returns.
- Provident funds are not considered national debt because they are essentially savings accumulated by individuals for their future retirement benefits.
- The government may regulate and supervise these funds, but it does not owe the accumulated funds as a liability.

3. Life Insurance Policies:
- Life insurance policies are financial contracts between individuals and insurance companies.
- They provide a death benefit to beneficiaries upon the insured person's demise or a maturity benefit if the policyholder survives the policy term.
- Life insurance policies are not considered national debt because they are private financial arrangements between individuals and insurance companies.
- The government does not owe the benefits provided by life insurance policies as a liability.

4. Long-term Government Bonds:
- Long-term government bonds are debt instruments issued by the government to raise funds from investors.
- They have a fixed maturity date and pay periodic interest to bondholders.
- Long-term government bonds are considered part of the national debt as they represent the government's borrowing obligations.
- These bonds are typically traded in financial markets and are subject to market forces.

In summary, while Provident Funds and Life Insurance Policies are not viewed as national debt, Long-term Government Bonds are considered part of a country's national debt. National Saving Certificates, on the other hand, are not typically considered national debt as they represent individuals' savings rather than government borrowing.