Let K be a compact
F-space such that |C∗(K)| = 2ω. Using the continuum hypothesis we characterize
those subspaces of K that are C∗-embedded in K. We also characterize the class of
extremally disconnected Tychonoff spaces of countable cellularity. As corollaries of
these theorems, using various set-theoretic hypotheses we characterize the
C∗-embedded, and the extremally disconnected C∗-embedded, subspaces of
βN.