Answer: oxygen
There is the s,p,d and f blocks, from groups 1-2 that is the s block, 13-18 that’s the p block, 3-12 is the d block and the f would be lanthanide(#57-71) and actinide (#89-103).
If 1mol ------- is ----------- 6,02×10²³
so x ------- is ----------- 1,39×10²⁴
A mole of any chemical compound contains the same number of molecules - about 6.022 × 10²³ molecules.
So, 1 mole of H₂O₂, 1 mole of C₂H₂ and 1 mole of CO contain the same number of molecules.
All of them are properties of compounds except III.
for I, compounds are chemically combined together, so to separate them, we must use chemical methods like electrolysis or applying heat. These requires large amount of energy.
For II, they're always fixed. For example, in water (H2O), the ratio of hydrogen and oxygen is always 1:8 in mass. If there's some extra added, the substance becomes mixture instead of compounds.
For IV, after you chemically combined elements or compounds together, their properties are completely different. For example, iron can be attracted to magnets, but iron II sulphide does not.
Boron would have the lower first ionization energy.
Be: 1s2 2s2
B: 1s2 2s2 2p1 -> electron from the p orbital is easier to eject than than electron from the s orbital.
