Completely stuck on last 4 clues
10 ac Does appropriate medical degree with element of chemistry (4) N - B -
17 ac After border exchange, old German immigrant
comes to this island (5) N - -O -
24 ac OneĀ“s work depressing, following dictator? (6)#
- - - i - t
18 dn cross with rings on raised layers centrally (7)
- - N - - - D
Many thanks.