Answer:
the answer is C acid dissolving limestone
Explanation:
That element is manganese. As they are in same horizontal row (period) and are next to each other. That is why they show same properties.
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Answer:

The air in the atmosphere consists of nitrogen, oxygen, which is the life-sustaining substance for animals and humans, carbon dioxide, water vapour and small amounts of other elements (argon, neon, etc.). Higher in the atmosphere air also contains ozone, helium and hydrogen.
The 5 main branches of chemistry are physics, analytical, biochemistry, organic chemistry, and inorganic chemistry.
A catalyst will speed up the activation energy and therefore speed up the reaction. The products will form fast because of this.