Atomic number is same as the number of protons in the element which is further equal to the number of electrons. As the number of electrons increases in the element, the atomic number of the element also increases.
In periodic table, elements are arranged in the groups, and these groups are columns starting from 1 to 18, elements are arranged in increasing order of atomic number. Elements are placed with difference of one atomic number.
First four elements present in the periodic table is:
atomic number is one (1).
atomic number is two (2).
atomic number is three (3).
atomic number is four (4).
Thus, the series of atomic numbers that represents the ordering of consecutive elements within the periodic table is the last option - 1, 2, 3, 4...
Hydrated salts are when salt crystals have water molecules bound. Anhydrous salts are when the water has been removed.
mass of water removed = hydrated salt - anhydrate salt
= 11.75 g - 9.25 g = 2.50 g
number of water moles = 2.50 g / 18 g/mol = 0.139 mol
number of cobalt (II) chloride moles = 9.25 g / 130 g/mol = 0.0712 mol
ratio of water moles to CoCl₂ moles - 0.139 mol / 0.0712 mol = 1.95
rounded off 2 moles of water for every 1 mol of CoCl₂
formula - CoCl₂.2H₂O
name - Cobalt(II) chloride dihydrate
We have Kc = 4.2 x 10^-2 (given but missing in the question)
and When the balanced equation for this reaction is:
PCl5(g) ↔ PCl3(g) + Cl2(g)
so, according to the Kc formula:
Kc = the concentration of products / the concentration of the reactants
so, to get the concentration of the reactants in equilibrium, the concentration of the products / the concentration of the reactants should equal the Kc value which is given in the question (missing in your question).
So by substitution in Kc formula:
Kc = [PCl3]*[Cl2] / [PCl5]
4.2 x 10^-2 = 0.18 * 0.25 /[PCl5]
∴[PCl5] = 0.18*0.25 / 4.2x10^-2 = 1.07
So the concentration of the reactants in equilibrim = 1.07
