下列离子符号书写正确的是 A．Ca+2 B．NH3+ C．S2- D．Fe2-

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问题选择题

下列离子符号书写正确的是

A．Ca⁺²

B．NH₃⁺

C．S^2-

D．Fe^2-

答案

答案：C

A、钙离子应为Ca²⁺，故A错误；

B、铵根离子应为NH₄⁺，故B错误；

C、硫离子为S^2-，故C正确；

D、铁离子为Fe²⁺，故错误．

故选：C．

选择题

--- Could you tell me ? --- Certainly. In 20 minutes.

A．when will the train to Beijing leave

B．when the train to Beijing would leave

C．when the train to Beijing left

D．when the train to Beijing will leave

单项选择题

儿童脑、脊髓照射剂量应低于成年人放射耐受量的()

A．10%

B．15%

C．20%

D．25%

E．40%