Which term of the A.P. 105, 101, 97, ………, is the first negative term?

Let the first negative term be n.

⇒ a_n < 0

⇒ a + (n - 1)d < 0

⇒ 105 + (n - 1)(-4) < 0

⇒ 105 - 4n + 4 < 0

⇒ 109 - 4n < 0

⇒ 4n > 109

⇒ n > $\dfrac{109}{4} = 27\dfrac{1}{4}.$

Given, n > $27\dfrac{1}{4}$.

So after 27^th term next terms will be negative so the first term to be negative will be 28^th.

Hence, 28^th term is the first negative term.