Lines 16a and 16b on 1040

Factual Questions
1

On the 1040 for pension information, is there a case that you can have zero on line 16a and something in 16b?

2

Yep–per the instructions

<<If your pension or annuity is fully taxable, enter it on line 16b; do not make an entry on line 16a.>>

PDF pg 25 http://www.irs.gov/pub/irs-pdf/i1040gi.pdf