### Clue: Rise in metal cost is radical (7)
### Answer: NITRATE 
 ### Explanation: Definition: radical
  **Reversal of**(rise, in a down clue) TIN(a metal) + RATE(a cost). 
Defn. and Answer: In chemistry, 2 or more atoms specifically arranged and behaving, as a group.  An example is the nitrate radical consisting of a nitrogen atom and 3 oxygen atoms.