Answer:
The answer to your question is letter A
Explanation:
Data
Mass ratio 1.62 to 1.00
Atomic mass Cr = 52 g
Atomic mass O = 16
Process
1.- Calculate the proportion Chromium to Oxygen to each possible solutions
a) CrO₃ = 
b) CrO₂ = 
c) CrO = 
d) Cr₂O =
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You might have meant hemiacetal, not hemicetal.
Acetals contain two –OR groups, one –R group and a –H atom. In hemiacetals, one of the –OR groups in acetals is replaced by a –OH group<span>.
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I would think that b would be the right answer