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Ответ:

Mr(H2) = 2Ar(H) = 2 а.е.м

Mr(N2O5) = 14 а.е.м×2+16 а.е.м×5 = 28+80=108

Mr(Al(OH)3)= 27 + 16×3 й 1×3 = 27 + 48 + 3 = 78 а.е.м

Mr(K2CO3) = 39×2 + 12×1 + 16×3 = 78 + 12 + 48 = 138 а.е.м