Step-by-step explanation
When the electronegativity difference is less than 4, it means the molecule is polar and when it is higher than 4, then it is non-polar.
For IF:
The electronegativity of Iodine = 2.66
The electronegativity of Flourine = 4.0
4.0 - 2.66 = 1.34
IF is polar
For CSe2:
The electronegativity of C = 2.5
The electronegativity of Se = 2.55
2.55 -2.5 = 0.5 but, The molecular geometry of CSe2 is linear with symmetric charge distribution on the central atom. Therefore CSe2 is non-polar.
Answer
IF is polar
CSe2 is non-polar