Which pair of elements from different periods shows the least difference in electronegativity?
Diagonal relationships minimize electronegativity differences. Be (1.5, period 2) and Al (1.5, period 3) have nearly identical values, unlike other pairs with larger gaps.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Anomalous Properties and Second Period and Chemical Reactivity