The answer to this question is 5
Answer: 
Explanation:
Electron gain enthalpy is defined as energy released on addition of electron to an isolated gaseous atom.
The amount of energy released will be maximum when the tendency to attract electrons is maximum. As flourine has atomic number of 9 and has electronic configuration of 2,7. It can readily gain 1 electron to attain stable noble gas configuration and hence liberates maximum energy.
A solid is hard and the molecules are packed together, a liquid can move around freely because the molecules aren't as packed together :)
Answer:
1. How do metals and non-metals react with acids?
Ans : Non metals does not react with acids while metals react with acids and produce hydrogen gas that burns with a 'pop'sound.
2. Write and explain the chemical equation for the reaction of magnesium with sulphuric acid and aluminium with hydrochloric acid.
Magnesium + sulphuric acid = Hydrogen + salt
Mg(s) + H2SO4 (aq) MgSO 4(aq) +H2 (g)
Aluminium + Hydrochloric acid = Hydrogen + Aluminium chloride
2Al(s)+6HCl(aq)→2AlCl3(aq)+3H2(g)