According to Raoult's low:
We will use this formula: Vp(Solution) = mole fraction of solvent * Vp(solvent)
∴ mole fraction of solvent = Vp(Solu) / Vp (Solv)
when we have Vp(solu) = 25.7 torr & Vp(solv) = 31.8 torr
So by substitution:
∴ mole fraction of solvent = 25.7 / 31.8 =0.808
when we assume the moles of solute NaCl = X
and according to the mole fraction of solvent formula:
mole fraction of solvent = moles of solvent / (moles of solvent + moles of solute)
by substitute:
∴ 0.808 = 0.115 / (0.115 + X)
So X (the no.of moles of NaCl) = 0.027 m
Answer:
(a) 
(b) Rubidium
Explanation:
Hello,
This titration is carried out by assuming that the volume of base doesn't have a significant change when the mass is added, thus, we state the following data a apply the down below formula to compute the molarity of the base solution:

Solving for the molarity of base we've got:

Now, we can compute the moles of the base as:

(a) Now, one divides the provided mass over the previously computed moles to get the molecular mass of the unknown base:

(b) Subtracting the atomic mass of oxygen and hydrogen, the metal's atomic mass turns out into:

So, that atomic mass dovetails to the Rubidium's atomic mass.
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Answer: Option (B) is the correct answer.
Explanation:
A covalent compound is a compound formed by sharing of electrons. And, in a covalent network solid atoms are bonded by covalent bonds in a continuous network that is extending throughout the material or solid.
This continuous arrangement of atoms are like a lattice.
For example, diamond is a covalent network solid in which carbon atoms are arranged in a continuous lattice like structure.
Hence, we can conclude that the statement all the atoms are covalently bonded to other atoms to form a lattice-like structure, best describes the structure of covalent network solids.