The figure shows three squares. Let the side of the smallest square be 1 unit.<br><br>&bull; ON represents the side of the smallest square = 1 unit.<br>&bull; QM = 2 &times; ON = 2 units (given).<br>&bull; From the figure, SR is the side of the smallest square = 1 unit.<br>&bull; Using the labelled lengths in the figure: ON = 3 cm, so SR = ON = 3 cm.<br><br>Final Answer: C: 3 cm