Step 1: Recall the condition for isotonic solutions.
Two solutions are isotonic if they have the same osmotic pressure.
Osmotic pressure is given by
\[
\pi=iCRT
\]
where
\[
i=\text{van’t Hoff factor}
\]
\[
C=\text{molar concentration}
\]
At the same temperature,
\[
iC
\]
must be equal for isotonic solutions.
Step 2: Check pair A.
For glucose:
\[
\text{Molar mass of glucose}=180\,g/mol
\]
\[
\frac{18}{180}=0.1\,M
\]
Glucose is non-electrolyte, so
\[
i=1
\]
Effective concentration:
\[
iC=1\times 0.1=0.1
\]
For urea:
\[
\text{Molar mass of urea}=60\,g/mol
\]
\[
\frac{6}{60}=0.1\,M
\]
Urea is also non-electrolyte, so
\[
i=1
\]
Effective concentration:
\[
iC=1\times 0.1=0.1
\]
Hence, pair A is isotonic.
Step 3: Check pair B.
For glucose:
\[
\frac{10}{180}=0.0556\,M
\]
For urea:
\[
\frac{10}{60}=0.1667\,M
\]
Their concentrations are different, so pair B is not isotonic.
Step 4: Check pair C.
NaOH dissociates completely:
\[
NaOH \rightarrow Na^+ + OH^-
\]
Thus,
\[
i=2
\]
Effective concentration:
\[
iC=2\times 0.01=0.02
\]
For glucose:
\[
i=1
\]
Effective concentration:
\[
1\times 0.02=0.02
\]
Hence, pair C is isotonic.
Step 5: Check pair D.
NaCl completely dissociates:
\[
NaCl \rightarrow Na^+ + Cl^-
\]
Thus,
\[
i=2
\]
Effective concentration:
\[
2\times 0.01=0.02
\]
For glucose:
\[
1\times 0.01=0.01
\]
These are not equal. Hence, pair D is not isotonic.
Step 6: Final conclusion.
Therefore, the isotonic pairs are
\[
\boxed{\text{A and C}}
\]