Answer:
•Matter is made up of smallest indivisible particle named as atom.
•All atom of same element have equal atomic mass and identical properties.
•Compounds are made up two or more different types of atoms.
•In a chemical reaction rearrangement of atoms takes place.
•Atoms of different elements differ in mass and size.
For a neutral atom, the number of positive protons is equal to the number of negative electrons and the charge is zero.
For this question, we see that the number of protons exceeds the number of electrons by 2, which means that this ion in a positively charged charged ion with charge of +2.
Answer:
7 valence electrons
Explanation:
Astatine has the atomic number 85. Thus, its electron configuration is:
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
As we can see, in the last level (6) it has 2 + 5 = 7 electrons, that is, astatine has 7 electrons in its valence shell. In the Lewis dot structure (attached) we write 3 pairs of electrons and 1 unpaired electron around the symbol of At.
Answer:

Explanation:
Hello!
In this case, considering that the mass of hydrazine is missing, we can assume it is 130.0 g (a problem found on ethernet). In such a way, since we need a mass-mole-atoms relationship by which we can compute moles of hydrazine given its molar mass (32.06 g/mol), then the moles of hydrogen considering one mole of hydrazine has four moles of hydrogen and one mole of hydrogen has 6.022x10²³ atoms (Avogadro's number); therefore, we proceed as shown below:

Notice 130.0 g has four significant figures, therefore the result is displayed with four as well.
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Cause (a substance) to be deposited in solid form from a solution.