Electrons in an atom can be classified as core electrons and valence electrons. Valence electrons are those electrons which are present in valence shell and participates in bond formation. While, Core electrons are all remaining electrons which are not present in valence shell, hence not take part in bonding.
Atomic number of Selenium (Se) is 34 hence it has 34 electrons with following electronic configuration;
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁴
From electronic configuration it is found that the valence shell is 4, and the number of electrons present in valence shell are 6. So,
Core Electrons = Total Electrons - Valence Electrons
Core Electrons = 34 - 6
Core Electrons = 28
Result:
There are 28 core electrons in Selenium.
D.) There must be an equal number of atoms of each element on both sides of the equation
Answer:
Force of attraction = 35.96 
N
Explanation:
Given: charge on anion = -2
Charge on cation = +2
Distance = 1 nm = 
m
To calculate: Force of attraction.
Solution: The force of attraction is calculated by using equation,
---(1)
where, q represents the charge and the subscripts 1 and 2 represents cation and anion.
k = 
F = force of attraction
r = distance between ions.
Substituting all the values in the equation (1) the equation becomes
Force of attraction = 35.96 N
Answer:
The answer to your question is Single replacement
Explanation:
Types of reaction in Chemistry
Synthesis two or more reactants combine to produce one single product
Decomposition one reactant splits producing two or more products
Single replacement One element replaces a similar one in a compound.
Double replacement Two compounds interchange their cations and anions.
Combustion one compound reacts with oxygen to produce carbon dioxide and water.
Reaction given
Fe⁺² + CuSO₄ ⇒ Cu + FeSO₄
This is a single replacement reaction
