Uranium-235 (U-235) has a half-life of around 700 million years. U-235 will decay into (after a series of separate decays) Pb-206 (Lead-206). A rock sample is found to have 6.25% (1/16) of its original U-235. a.) How many half-lives have passed?

b.) How many years has this taken?

c.) If there were 30 grams of U-235 originally, how many grams would be left now?

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 

Dsolubility let me know if you have any other questions for chemistry

Ibelieve the answer 4 moles