Rank the following transition metals in order of increasing atomic radius.
(a) Tc (b) Ru (c) Mo (d) Nb
Provide an explanation for the observed trend.

• A. Ru < Tc < Mo < NbThe observed trend of decreasing atomic radii from left to right across the period is caused by the increasing nuclear charge from left to right across the period. 
• B. Nb < Mo < Tc < RuThe observed trend of decreasing atomic radii from left to right across the period is caused by the increasing nuclear charge from left to right across the period. 
• C. Ru < Tc < Mo < NbThe observed trend of increasing atomic radii from left to right across the period is caused by the decreasing nuclear charge from left to right across the period. 
• D. Nb < Mo < Tc < RuThe observed trend of increasing atomic radii from left to right across the period is caused by the decreasing nuclear charge from left to right across the period. 

Answer: (A)