Compare Fractions: Find the Missing Symbol Between 2/7 and 4/21

To solve this problem, we'll follow these steps:

• Step 1: Find the common denominator for the fractions.
• Step 2: Convert each fraction to this common denominator.
• Step 3: Compare the resulting fractions by examining their numerators.

Now, let's work through each step:
Step 1: Identify the denominators of the fractions. We have $7$ and $21$. The least common multiple (LCM) of $7$ and $21$ is $21$, which we'll use as the common denominator.

Step 2: Convert $\frac{2}{7}$ to a fraction with a denominator of $21$.
We achieve this by multiplying both the numerator and the denominator by $3$:
$\frac{2}{7} = \frac{2 \times 3}{7 \times 3} = \frac{6}{21}$.

The second fraction, $\frac{4}{21}$, already has the denominator $21$.

Step 3: Compare the numerators of the fractions $\frac{6}{21}$ and $\frac{4}{21}$.
We see that $6 > 4$.

Since $6 > 4$, it follows that $\frac{6}{21} > \frac{4}{21}$ and thus $\frac{2}{7} > \frac{4}{21}$.

Therefore, the correct sign to place between $\frac{2}{7}$ and $\frac{4}{21}$ is $\mathbf{>}$.

Hence, the solution to the problem is $>$, which corresponds to choice $2$.