Asolution made by dissolving 9.81 g of a nonvolatile nonelectrolyte in 90.0 g of water boiled at 100.37degree c at 760 mm hg. what is the approximate molecular weight of the substance? (for water, kb = 0.51 degree c/m)

Answer is: molecular weight of the substance is 79.75 g/mol.
Kb(H₂O) = 0,51°C/m.
T(nonvolatile nonelectrolyte) = 100.37 °C.
T(H₂O) = 100°C.
ΔT = 100.37°C - 100°C.
ΔT = 0.37°C.
ΔT = b(nonvolatile nonelectrolyte) · Kb(H₂O).
b(nonvolatile nonelectrolyte) = ΔT ÷ Kb(H₂O).
b(nonvolatile nonelectrolyte) = 0.37°C ÷ 0.51°C/m.
b(nonvolatile nonelectrolyte) = 1.372 mol/kg.
b - molal concentration.
b = n(nonvolatile nonelectrolyte) / m(H₂O).
n = 1.372 mol/kg · 0.09 kg = 0.123 mol.
M(nonvolatile nonelectrolyte) = m / n.
M = 9.81 g ÷ 0.123 mol = 79.75 g/mol.

The Rashidun Caliphs (Rightly Guided Caliphs; Arabic: الخلفاء الراشدون‎ al-Khulafāʾu ar-Rāshidūn), often simply called, collectively, "the Rashidun", is a term used in Sunni Islam to refer to the 30-year reign of the first four caliphs (successors) following the death of the Islamic prophet Muhammad, namely: Abu Bakr, Umar, Uthman ibn Affan, and Ali of the Rashidun Caliphate, the first caliphate. The caliphate of Hasan ibn Ali is sometimes also considered to be Rashidun as well but since it was merely a six month period it is not mentioned categorically. The concept of "Rightly Guided Caliphs" originated with the later Abbasid Caliphate based in Baghdad. It is a reference to the Sunni imperative "Hold firmly to my example (sunnah) and that of the Rightly Guided Caliphs" (Ibn Majah, Abu Dawood).