Answer:- 
Explanations:- Alkanes are non polar molecules as these only have carbons and hydrogens. Electron negativity difference of C and H is very low and it makes them non polar. These have weaker London dispersion forces.
The forces of attraction becomes stronger in alkanes as the number of carbon increases because the surface area as well as molecular weight of the alkanes increases with an increase in number of carbons.
Butane has four carbons, propane has three carbons, ethane has two and methane has only one carbon, So, the strongest to weakest order of inter molecular forces is butane > propane > ethane > methane .
C. Difficulty in concentrating.
One of the common symptom for Bipolar disorder is the difficulty in concentration or decreased ability to think and indecisiveness. They tend to make wrong decisions because of this symptom. And because they do not think thoroughly, bipolar disorder patients have poor decision making.
Molar mass of CaCl2 = 40+ ( 35.5 ×2)=110
Mr of Ca(OH)2 = 40+ (16+1)×2 =74
%of Ca = (40÷ 74)×10=...
1 m = 100cm...
1cm = (1÷100) m
So 45.5 cm = 45.5 ×(1÷100) =....
1km = 1000m
1m = 100 cm
1cm =10mm
So 1km = 1000×100×10 mm
Now convert