15.6gNa2x含Na+0.4mol，则Na2x的摩尔质量为――x的相对原子质量为―― 过程

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n(Na2X) = 1/2 n(Na) = 0.2mol
M(Na2X) = 15.6/0.2 = 78 g/mol
X的相对分子携族困质量辩念穗余= 78 - 46 = 32

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