I am in my second trimester and lately I have developed a craving for smelling chalk? Is it normal?

Yes, it's a bit worrying and seems that you are suffering from Pica disorder. Pica is an eating disorder and it causes an uncontrollable desire to eat substances with little or no nutritional value. Often pregnant women who are deficient in iron or zinc have craving to eat substances other than normal food such as chalk or clay. Eating non-food substances is potentially harmful to both you and your baby. Please visit your doctor.