How many minimum squares must be shaded to make the given figure symmetric?

Which of the following squares would you shade to make the figure symmetrical?

Read the statements given below and identify the correct option.

(i) A parallelogram has only one line of symmetry.

(ii) A square and a rectangle have the same number of lines of symmetry.

(iii) The diameter of a circle is its line of symmetry.

What is the least number of squares that must be added so that the line $\text{MN}$ becomes a line of symmetry?

What is the smallest number of squares that must be shaded so that the line $\text{AB}$ becomes the line of symmetry?