Which of the following optically active ketones lose their optical activity when stirred with dilute aqueous $\mathrm{NaOH}$ for some time?

Racemisation by base needs the stereocentre to be an alpha carbon bearing H, because enolisation destroys it (the enolate is planar there). In 2-methylcyclohexanone, C-2 is alpha. In 3-methylpentan-2-one, C-3 is alpha. In 3-methylcyclohexanone and 4-methylhexan-2-one the stereocentre is beta and is untouched, so these keep their activity.