The answer is sodium (Na)
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Electronegativity is the tendency of an element to attract the bonded electrons towards itself. In a group, as the atomic radius increases electronegativity decreases as the outermost electron is far away from the nuclear attraction. In a period, the atomic size decreases. So, the effective nuclear charge experienced by the outermost shell increases. Therefore, across a period the electronegativity increases as the increased effective nuclear charge leads to the attraction of bonded electrons with greater ease.
Therefore the correct answer is <u>c</u>, electronegativity tends to increases across a period.
Explanation:
On a periodic table, the atomic size is depicted by the radius of the atom.
Across a period, the atomic radius reduces progressively from left to right.
Down the group from top to bottom, atomic radii increases progressively.
For the ionization energy, from left to right, across the period, it increases progressively and down a group it reduces.
These two trends are related in that as the atomic radius decreases across the period there is an increasing nuclear charge which is not compensated for by the the successive shells of electrons being added. This also similar down the group.
<span>1.15x10^24 molecules of hypothetical substance b
Making the assumption that each molecule in hypothetical substance a reacts to produce a single molecule of hypothetical substance b, then the number of molecules of substance b will be the number of moles of substance a multiplied by avogadro's number. So
Moles hypothetical substance a = 29.9 g / 15.7 g/mol = 1.904458599 moles
This means that we should also have 1.904458599 moles of hypothetical substance b. And to get the number of atoms, multiply by 6.0221409x10^23, so:
1.904458599 * 6.0221409x10^23 = 1.146892x10^24 molecules.
Rounding to 3 significant figures gives 1.15x10^24</span>
