Lifetime - the period of execution time during which the element is available for use.

生存期-执行时间的周期，元素在此期间可供使用。

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In each period, the atomic number of each element is increasing.

每个周期中元素的质子数从左到右递增。

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In each period, the atomic number of each element is increasing.

每个周期中元素的质子数从左到右递增。

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