Briefly explain why the bulk temperature of the water remains low (at room temperature)

Can someone me with 3 and 4 plz. this is for masteries test.

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.

Select the word from the list that best fits the definition the nuclear family into which a person is born or adopted.