Correct Answer  Option 3 : 35
Concept:
Control of deflection:
The vertical deflection limit may generally be satisfied if
(a) Basic span to effective depth ratio for span up to m is
Types of Beams: \(\frac{{{\rm{span}}}}{{{\rm{effective\;depth}}}}\)
For cantilever → 7
For simply supported → 20
For continuous → 26
(b) For span > 10 m effective depth \( = \frac{{{{\left( {{\rm{span}}} \right)}^2}}}{{10 \times {\rm{A}}}}\)
Where ‘A’ is span to effective depth ratio for span up to 10 m.
(c) Deflection check for two way slab:
Support Condition

Span/overall depth

Mild steel

Fe415/Fe500

Simply supported

35

28

Continuous

40

32

So, From the above table It is clear that Span/depth ratio for two way slab should not be greater than 40. But From the given options, 35 is the closest one.