Answer:
Everything is composed of atoms! which are the indivisible building blocks of matter and cannot be destroyed. All atoms of an element are identical. The atoms of different elements vary in size and mass.
Explanation:
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The enthalpy change : -196.2 kJ/mol
<h3>Further explanation </h3>
The change in enthalpy in the formation of 1 mole of the elements is called enthalpy of formation
The enthalpy of formation measured in standard conditions (25 ° C, 1 atm) is called the standard enthalpy of formation (ΔHf °)
(ΔH) can be positive (endothermic = requires heat) or negative (exothermic = releasing heat)
The value of ° H ° can be calculated from the change in enthalpy of standard formation:
∆H ° rxn = ∑n ∆Hf ° (product) - ∑n ∆Hf ° (reactants)
Reaction
2 H₂O₂(l)-→ 2 H₂O(l) + O₂(g)
∆H ° rxn = 2. ∆Hf ° H₂O - 2. ∆Hf °H₂O₂

I do not see any mistakes so I think you’re good!
Answer:
See explanation
Explanation:
Atomic size increases down the group due to the addition of more shells.
As more shells are added and repulsion of inner electrons become more significant, atomic size increases down the group. However, across the period, atomic size decreases due to increase in effective nuclear charge without any increase in the number of shells. This causes increased attraction between the nucleus and the outermost shell thereby decreasing the size of the atom.
Ionization energy decreases down the group because the outermost electron is more shielded by inner electrons making it easier for this outermost electron to be lost. Across the period, ionization energy increases due to increase in effective nuclear charge which makes it more difficult to remove the outermost electron due to increased nuclear attraction.
Answer:
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