For 25 squares of size 1x1 you’d need a square of size 5x5. The square into which 17 1x1 squares fit is smaller than 5x5, so you can’t fit 25 squares into it.
You raised the packing coefficient by ⅝ to squeeze one extra square in with all that wasted space, so don’t argue that 25 squares has a packing coefficient of 5. Another ⅜ will get you an extra 8 squares, and no wasted space.
For 25 squares of size 1x1 you’d need a square of size 5x5. The square into which 17 1x1 squares fit is smaller than 5x5, so you can’t fit 25 squares into it.
Do I need to tap the sign?