He concentration of pb2+ in a commercially available standard solution is 1.00 mg/ml. what volume of this solution should be diluted to 5.0×102 ml to produce a solution in which the concentration of pb2+ is 0.055 mg/l?

This can be directly solved using the formula:

C1 V1 = C2 V2

where C is concentration and V is volume

 

1.00 mg/ml * V1 = 0.055 mg/1000 ml * (5.0 x 10^2 ml)

V1 = 0.0275 ml

 

So 0.0275 ml is needed to be diluted to 5.0 x 10^2 ml

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.