Why do calcium ions make water hard but sodium ions do not

Options

(a) Calcium forms insoluble compounds with stearate ions present in soap
(b) Sodium forms insoluble compounds with stearate ions present in soap
(c) Calcium forms soluble compounds with stearate ions present in soap
(d) Both calcium and sodium forms insoluble compounds with stearate ions present in soap

Correct Answer:

Calcium forms insoluble compounds with stearate ions present in soap

Explanation:

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