What do you think
makes the sky blue?

The color of sunlight ; True. Sunlight contains blue light. But clouds are white when the sun shines on them. What feature of the sky makes it blue?
The color of the air ; Does the moon appear blue at night? It would if the air was blue.
Something else ;; Correct.

The sky is not always blue.

It is black at night. ; So the blue color requires sunlight.
It is orange at sunset. ; So the blue color requires the sunlight to pass through relatively little, clean air.
It is white or gray on a cloudy day. ; So the blue color depends on the air not being full of condensed water.
It is blue at midday on a clear day. ;; And moreover, it is blue in every direction.

What does this tell us
about the blue light
coming from the sun?

It is reflected ; No.  This would cause the blue color to be brighter in one direction, just as we see a reflection of the sun in a mirror only from a certain angle.
It is refracted ; No, like reflection, this would cause the blue color to bend in one direction, just as we see the blue color in a rainbow only from a certain angle.
It is scattered ;; Correct.

Air absorbs some of the blue light from the sun.
That light is then radiated in random directions.

This is called Rayleigh Scattering ; after the English physicist Lord Rayleigh
[http://en.wikipedia.org/wiki/Rayleigh_scattering Learn more];
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