Use the References to access important values if needed for this question. Radioactive decay can be described by the following equation where is the original amount of the substance, is the amount of the substance remaining after time , and is a constant that is characteristic of the substance. For the radioactive isotope iron-55, is . If the original amount of iron-55 in a sample is 74.0 mg, how much time is needed for the amount of iron-55 that remains to fall to 32.7 mg? years

Explanation:

from the Radioactive decay equation ; lnA = ln Ao - ktAo = original amount of substance = 74mgwhere A = is the amount of the substance remaining after time t = 32.7mg, k = is a constant that is characteristic of the substance = 2.67 x 10^-1 years^-1t = ?

All radioactive substances follow the first order kinetics, as such the rate constant for first order is given as , k = 1/t ln[Ao/A]

hence t = 1/k ln[Ao/A]plugging the values in the equation; t = 1/0.267 x ln [74/32.7]t = 3.745 ln(2.2629)t = 3.05years is the time needed

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.

Replicate prove reliability and validity