Naruto Shippuden episode 15
episode 76
Sometime during Season 1 - 3
In the anime, it's a flashback in episode 161. Naruto teaching Konohamaru the rasengan was actually done off screen. In the flashback, Naruto is describing the rasengan to Konohamaru, who thinks he's about to teach him another sexy jutsu. Hope that helps.
Naruto episode 453 isn't out yet.
Episode 135 Naruto 1st Season
If you're talking about 'Naruto' then its season 4. If you're talking about 'Naruto Shippuden' its season 5.
For naruto shippuden its on episode 107
I am thinking that it is Naruto episode 79 the last episode of 4th season.
Their is an episode intitled "The Death of Naruto" (episode 165 season 4 on hulu).
Episode 208
In fact, naruto shippuden is the continued season of naruto in japan
Surprise Attack! Naruto's Secret Weapon! (episode 45 season 1).
at the end of Naruto 1st season Episode no 220