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【单选题】
放射性同位素钍 Th经一系列α、β衰变后生成氡 Rn,以下说法正确的是A.
每经过一次α衰变原子核的质量数会减少2个
B.
每经过一次β衰变原子核的质子数会增加1个
C.
放射性元素钍 Th的原子核比氡 Rn原子核的中子数少4个
D.
钍 Th衰变成氡 Rn一共经过2次α衰变和3次β衰变
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