Ok,
1. You need to find out how many moles of Hydrogen there are in 1g. so using n=m/M it comes out to 0.5 mol. So therefore the number of atoms is 0.5* 6.02*10^23, the avogadro's constant. Ok now you have figured out the number of atoms for 1 hydrogen, so in a hydrogen molecule there are 2 hydrogen atoms so you go, (0.5* 6.02*10^23)* 2. This gives you the number of atoms in the hydrogen molecule. Ok now looking through the options you can see that Ne is 1 atom and when you calculate the number of moles it comes out to 1. So therefore 1*6.02*10^23 should equal (0.5* 6.02*10^23)* 2. that's how you figure it
out.
2. For greatest polarity you have to look at the charge density of an ion. the Al3+ has a charge of +3, and because it has a large nuclear charge,( because it has more protons then electrons it would attract the outer electron with greater strength decreasing the size of the ion. So therefore overall the charge of the ion/ the size gives you the polarising ability of the ion. So out of all the options this has the greatest charge density so it would be the most polarising.
3. This is explained within the brackets of the previous question. the size of the ion depends on the nuclear charge and the shielding and repulsion the valence electrons of each ions has. When there is a greater effective nuclear charge, more protons than electrons it hold the ion more closely, but if there is more electrons than protons then the electrons are not held aas strongly and there is repulsion among the electrons as well.
Hope i answered your questions
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