Cho 1 lượng oxit kim loại nhóm IIA tác dụng vừa đủ với dd HCl 10% thì sau phản ứng thu được dung dịch muối có nồng độ 12,34 %. Xác định công thức của oxit kim loại. (Cho Be=9, Mg=24, Ca=40, Sr=88, Ba=137)

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