Same as Fig. 16 for the SiO (J = 5−4)/(2−1) ratio. The error is estimated to be 15% for N(H₂), while for the line ratio the error is calculated from the noise in the two lines: . Altogether 100 sources are shown on the plot. Sources classified as clumps with embedded H II regions are shown in blue, red circles show the infrared-bright clumps, while green corresponds to the infrared-quiet clumps.