Which of the following causes the formation of ionic bonds

a. two atoms sharing electrons
b. one atom transferring electrons to another atom
c. an element undergoing radioactive decay
d. fission

b. One atom transferring electrons to another atom

Explanation: An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.

Covalent bonds are formed by sharing of electrons between non metals

For example, In calcium iodide the one electron from calcium metal gets transferred to iodine atom and thus form an ionic bond to give

Electronic configuration of calcium:

Calcium atom will lose two electron to gain noble gas configuration and form calcium cation with +2 charge.

Electronic configuration of iodine:

Iodine atom will gain one electron to gain noble gas configuration and form iodide ion with -1 charge.

Northern neighbors crossed into Northern China and occupied large Chinese territory. Song rulers were forced to move the imperial court south to Hangzhou, the Song also lost control over Tibet. Mongols also overthrew the Song and set a new Mongol dynasty

Explanation: