By interchanging which two signs the equation will be correct?
$$11 + 16 \times 12 \div 4 - 2 = 21$$

Given, 11+16 $$\times$$ 12 $$ $$ $$\div$$ 4 $$ $$ - 2 = 21

These type of questions can be quickly solved by checking options.

So,from the options we get option A would be correct.

On solving,11+16-12 $$\div $$ 4 $$ $$ $$\times$$2 $$ $$

$$\Rightarrow$$  27 - 6 = 21.

From option (b), we will get the negative value which is not possible.

From options (c) and (d), we will get the fractional values which is not possible.