What is the correct way to represent the ionic compound sodium fluoride

What is common about these molecules? a.their atoms are held together by covalent bonds. b.they are all made up of the same two atoms. c.their atoms are held together by ionic bonds. d.they are all made up of oxygen atoms only.

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

8.98 dm3 of hydrogen gas is collected at 38.8 °c. find the volume the gas will occupy at -39.9 °c if the pressure remains constant.