Becquerel’s experiment consisted of four steps. 1. Get a sample of a uranium salt.
2. Expose the salt to sunlight.
3. Expose photographic plates to the salt.
4. Develop the plates.

A change in which step led to Becquerel’s discovery of radioactivity?
1
2
3
4

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.