In a HP 4th term is 1/11and 24th element is 3/23.find 7th and 19th term?

The reciprocals form an AP, so for that sequence,

a+3d = 11
a+23d = 23/3
a = 23/2
d = -1/6

Now you can find the desired terms:

H7 = 1/(a+6d)
H19 = 1/(a+18d)