What would the formula of an ionic compound made up of Calcium and Oxygen be?

What information does a complete ionic equation give that the balanced equation doesn’t show?

An unknown substance has been shown to have weak covalent bonds. which of the following is most likely a property of this substance? a. high ph b. high conductivity c. low melting point d. low flammability

Stoichiometry- i need with 14 and 15! an explanation would be appreciated!