Parsons agrees that the Ministry of Plenty did a "good job this year". (pg.53) Why is the question that he asks Winston at that point ironic in 1984?

To answer this, just look at two things.  First, what
should it look like if the Ministry of Plenty did a good
job?  Second, what does Parsons ask Winston?

If the
Ministry of Plenty is truly doing a good job, you would think that the people would be
well off.  They should be well fed and they should have (at the very least) all the
essentials of life.

But look at what Parsons asks Winston. 
He asks Winston whether he has any spare razor blades he could give Parsons.  This means
that there is a razor blade shortage -- Winston says he's been using his for 6 weeks and
no one thinks that's strange.

To me, this is ironic because
Parsons somehow believes the Ministry is doing a great job when, at the same time, he
can't even get something as basic as a razor blade.  That's ironic because the two ideas
(Ministry doing great; he can't get a razor blade) are so
contradictory.