\textbf{207-} If 0.1 mol of the salt $\mathrm{Na_2SO_4 \cdot 8H_2O}$ is heated and its weight decreases by approximately 18.9 percent, $x$ in the chemical formula of the remaining solid $(\mathrm{Na_2SO_4 \cdot xH_2O})$ is approximately which of the following?
$$(\mathrm{Na = 23\ ,\ S = 32\ ,\ O = 16\ ,\ H = 1 : g.mol^{-1}})$$
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(1) 3 \qquad (2) 4 \qquad (3) 5 \qquad (4) 6
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