Q.Which one of the following rotates the plane polarized light towards left? (NEET Phase – II)

Step 1. The question asks which compound rotates plane-polarised light to the LEFT, i.e. which one is levorotatory. Levorotatory compounds are always marked with a (-) sign; dextrorotatory compounds are always marked with a (+) sign -- this sign is a directly measured property, completely separate from the D/L configurational label.

Step 2. Check each option's sign: (a) D(+) Glucose carries a (+) sign, so it is dextrorotatory (rotates right).

(b) L(+) Glucose also carries a (+) sign -- note that the L configurational label does NOT force a (-) rotation; L(+)-glucose is still dextrorotatory.

(c) D(-) Fructose carries a (-) sign, so it is levorotatory (rotates left) -- this is, in fact, natural fructose, sometimes called levulose for exactly this reason.

(d) D(+) Galactose carries a (+) sign, so it is dextrorotatory.

Step 3. Only option (c) carries the (-) sign that corresponds to left (anticlockwise) rotation of plane-polarised light.

Read off the (+)/(-) sign printed directly on each option -- that sign alone tells you the rotation direction; the D/L label describes a different, independent property (configuration relative to glyceraldehyde).

• Assuming the D label always means dextrorotatory and the L label always means levorotatory -- the configurational D/L label and the rotational (+)/(-) sign are independent properties, as options (b) L(+) and (c) D(-) both demonstrate.