Answer is 0.7 g
Reason: Given: mass of Fe = 5.60 gWe know that, half life of Fe-53 = t1/2 (Fe-53) = 8.51 min.
Thus, after 25.53 mins, number of half life passed = 25.53/8.51= 3
Now, Amount left after first half life = 5.60g/2 = 2.80 g
Amount left after second half life = 2.80g/2 = 1.40 g
Amount left after third half-life = 1.40g/2 = 0.7g.
Answer: 
Explanation:
Depression in freezing point is:
where,
= freezing point of solution = ?
= freezing point of solvent (cyclohexane) = 
= freezing point constant of solvent (cyclohexane) = 
m = molality
i = Van't Hoff factor = 1 (for non-electrolyte)
= mass of solute (biphenyl) = 0.771 g
= mass of solvent (cyclohexane) = 25.0 g
= molar mass of solute (biphenyl) =
Now put all the given values in the above formula, we get:
Therefore, the freezing point of a solution made by dissolving 0.771 g of biphenyl in 25.0 g of cyclohexane is
