The decay of the isotope iodine-131 is first-order with a rate constant of 0.138 d−1. all radioactive decay is first order. how many days will it take for 90% of the isotope to decay to xe-131?

16.7 days

Explanation:

We are given;

A radioactive isotope Iodine-131`

The decay rate is 0.138 d⁻¹

The percent decayed is 90%

We are suppose to calculate the number of days for the decay.

Using the formula;

Where, is the initial concentration and is the new concentration.

Rearranging the formula;

Assuming the initial concentration is x, then the final concentration after 90% decay will be 0.10x

Therefore;

Time = 16.7 days

Therefore, it will take 16.7 days for 90% of I-131 to decay to Xe-131

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic