Which of the following orders of elements is correct in terms of decreasing atomic size?

Atomic radius is defined as the distance between centre of nucleus and outermost shell, which contains electrons in an isolated atom. On moving from left to right in a period, atomic radius decreases. This is because as we move from left to right, the atomic number of each succeeding element increases by 1. This means that the number of protons in the nucleus and the number of electrons in the extra part of the nucleus increase by 1. The electrons are added to the same shell, but the addition of an extra proton in the nucleus increases the nuclear charge, which attracts the electrons closer to the nucleus, thereby decreasing the atomic radius, whereas on moving down a group, atomic radius increases as the number of shells increases. F, Cl and Br belong to group 17 and on moving down the group from F to Br, their atomic size will increase. So, the correct order in terms of decreasing atomic size is: Br > Cl > F. Similarly, Li, Na and K belong to group 1 and on moving down from Li to K, their atomic size will increase. So, their correct order is: K > Na > Li. B, C and N belong to the 2^nd period and on moving across the period from B to N, their atomic size will decrease. So, their correct order is: B > C > N. S, P and Si belong to the 3^rd period and on moving from Si to S, the atomic radius will decrease. So, their correct order in terms of decreasing atomic size is: Si > P > S. Therefore, only option (3) is correct.