Answer:
Protons and neutrons which packed tightly into central core of the atom.
Explanation:
Atoms are composed of three subatomic particle; electron, proton and neutron. Electrons are negatively charged, protons are positively charged whereas neutrons are neutral, hence does not have any charge.
Out of three, protons and neutrons are present in the nucleus of the atom.
Nucleus is the central part of the atom possessing most of the mass of the atom. In the nucleus, protons and neutrons are tightly packed with the help of nuclear force.
Electrons are present around the nucleus also called electron cloud.
Therefore, nucleus are composed of protons and neutrons which packed tightly into central core of the atom
Answer : The mass of water produced will be 32.78 grams.
Explanation : Given,
Mass of 
= 21.9 g
Molar mass of = 72.15 g/mole
Molar mass of 
= 18 g/mole
First we have to calculate the moles of .
Now we have to calculate the moles of .
The balanced chemical reaction will be,
From the balanced reaction we conclude that
As, 1 mole of react to give 6 moles of
So, 0.3035 moles of react to give 
moles of
Now we have to calculate the mass of .
Therefore, the mass of water produced will be 32.78 grams.
If a sample is packed poorly, the sample will not heat evenly and will take longer to melt.
Answer:
Fe is just the shortened version of Iron whereas Fe2+ is a positive ion,cation to be more specific
