The simple interest on a sum of money is 1/9 of the principal and the number of years is equal to the rate percent per annum. The rate percent per annum is:

The correct option is 3.33%.

Let the principal amount of money be represented by $P$ and the rate percent per annum be represented by $R$.
According to the problem, the number of years, which we can represent as $T$, is numerically equal to the rate percent per annum. Therefore, we have:
$T=R$

We are also given that the simple interest (SI) is $\frac{1}{9}$ of the principal. This can be written as:
$\mathrm{SI}=\frac{P}{9}$

The standard formula for calculating simple interest is:
$\mathrm{SI}=\frac{P\times R\times T}{100}$

By substituting the values of $\mathrm{SI}$ and $T$ into the formula, we get:
$\frac{P}{9}=\frac{P\times R\times R}{100}$

We can simplify this equation by dividing both sides by $P$ (assuming $P\ne 0$):
$\frac{1}{9}=\frac{R^2}{100}$

Now, solving for $R^2$ by multiplying both sides by 100:
$R^2=\frac{100}{9}$

Taking the square root of both sides to find the rate $R$:
$R=\sqrt{\frac{100}{9}}$
$R=\frac{10}{3}$

Converting the fraction to a mixed number or decimal value:
$R=3\frac{1}{3}\%\approx 3.33\%$

Thus, the rate percent per annum is 3.33%.