What effect do calcium ions have on the water in ecosystems?

They add to its hardness.

Explanation:

Hello,

Water in ecosystems are likely to have dissolved metallic cations such those alkalies and alkaline earth metals form when present in aqueous systems, in this manner, more specifically speaking, calcium ions promote the formation of unsoluble salts such as calcium carbonate, which lead to the increase of the water's hardness that accounts for such cation's content into the water. Therefore, among the following options:

A. They reduce its pH.

B. They decrease its salinity.

C. They add to its hardness.

D. They increase its acidity.

The correct is C. They add to its hardness.

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