Correct Answer - Option 4 : 10%

**Given:**

SI is equal to the Principal,

The number of years is equal to the rate of interest

Concept Used:

SI = (P × N × R)/100,

Where,

P is Principal,

SI is Simple Interest,

N is total number of years,

R is rate

**Calculation:**

SI = P, and R = N,

Using in the formula,

P = (P × R × R)/100

⇒ 100 = R^{2}

⇒ R = 10%

**∴ Rate of interest is 10%.**