Good trustees have the knack of asking questions that lead to good decisions. Some questions might be insightful; others innocent; many will be probing; and others will be from 'outside the box'. There is no such thing as a bad question if it is intended to be constructive and relevant.
When a board receives recommendations, it is questioning that inspires confidence in a proposal or highlights the need for a reappraisal. Many chairs understand this and ensure that time is devoted to questions from all trustees.
Searching for instant answers at board meetings is to be avoided. This could lead to trustees asserting their particular views and opinions, when it is questions that often lead to better decisions.
It is helpful to look at what questions other boards are asking. A number of helpful leaflets can be found on the Charity Commission's website. Two good places to start might be Questions to Consider at Key Stages in the Life of a Charity and The Economic Downturn: 15 Questions Trustees Need to Ask.