There are 24 valance electrons in the compound.
<h3>What are valence electrons?</h3>
We know that the valence electrons are those that are found on the valence shell of an atom. There are four atoms that can be seen in the compound that is under consideration. The atoms are selenium, bromine (2 atoms) and oxygen.
Given that there are seven valence electrons in bromine and six valence electrons in oxygen and selenium. We have;
2(7 electrons of bromine) + 6 electrons of oxygen + 4 electrons of Se
= 24 electrons
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Answer:

Explanation:
Given that:
Half life = 30 min
Where, k is rate constant
So,
The rate constant, k = 0.0231 min⁻¹
Using integrated rate law for first order kinetics as:
Where,
is the concentration at time t
is the initial concentration
Given that:
The rate constant, k = 0.0231 min⁻¹
Initial concentration
= 7.50 mg
Final concentration
= 0.25 mg
Time = ?
Applying in the above equation, we get that:-

A, B and D should be the ones you should check
Explanation:
The structure of Ferrarrisite Ca5(HAs O4)2(AsO4)2
The net ionic equation of the reaction could be determined by cancelling out the like ions between both sides of the reaction. These ions are called spectator ions. They are called as such because they do not actively participate in the reaction. The spectator ions are Na+ and Cl-. When you cancel those, the equation would become letter D.