An atom will form a chemical bond with another atom if 1. the other atom is identical to it.
2. their outer energy levels are already
filled.
3. ions can be formed.
4. the resulting molecule is more stable.

3. ions can be formed.

Explanation:

An atom will form a chemical bond with another atom if ions can be formed.

Ions are the charged atom or molecule (cation and anion) and are formed due to an imbalance between the number of protons and electrons between two different atoms. The chemical bond form between two atoms when electrons transfer from one atom to another atom. The atom that gains electrons becomes a negatively charged ion (anion) and the electron loses electron become cation, positively charged.

Hence, the correct answer is "3. ions can be formed."

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"