I was tempted to pass this question up...tone is one of those things that can be a bit subjective and requires some thought. All in all, I find it to be one of the harder elements of fiction to understand. But then I thought, what the heck. It is obviously a hard question for you, too, so we can both struggle with it together. Let's look at the tone in the first poem:
I'm Nobody, Who Are You!
I'm nobody! Who are you?
Are you nobody, too?
Then there's a pair of us — don't tell!
They'd banish us, you know.
How dreary to be somebody!
How public, like a frog
To tell your name the livelong day
To an admiring bog!
In this poem, the tone seems largely humorous and familiar. It's like a sly joke between two friends. "They'd banish us, you know." "How dreary to be somebody!" These are whimsical statements that are meant to be light and entertaining.
Now for the tone of poem 2:
I Heard a Fly Buzz When I Died
I heard a fly buzz when I died;
The stillness round my form
Was like the stillness in the air
Between the heaves of storm.
The eyes beside had wrung them dry,
And breaths were gathering sure
For that last onset, when the king
Be witnessed in his power.
I willed my keepsakes, signed away
What portion of me I
Could make assignable,-and then
There interposed a fly,
With blue, uncertain, stumbling buzz,
Between the light and me;
And then the windows failed, and then
I could not see to see.
The tone of this poem, it could be argued, is "distracted acceptance." Notice how the person in the poem seems pretty at peace with the idea of dying. She is not angry sounding, fighting against death...she is simply accepting. She shows little emotion at her upcoming demise.
And the fly...notice the way that even at a moment like death something little like a fly buzzing distracts the narrator. She is unable to concentrate on thoughts of her ending because of its buzzing. There are no final words or revelations, just the idea that the fly "ruins" what otherwise would have been a quite slipping away. Maybe the tone should be "irritated acceptance?"
Now, poem 3. I'm not going to put the whole poem in because it is a bit longer:
Because I Could Not Stop For Death
Because I could not stop for Death,
He kindly stopped for me;
The carriage held but just ourselves
This poem has a tone that is similar to the second one, but without the irritation. The narrator of this poem seems quite relaxed with the thought of death. Indeed, death seems almost a welcome event. Death comes in the shape of a cordial force, an escort. Compare that with the tone of the last poem, where the fly as an irritant ruins the relaxed dying process, and you can see the difference between the two.
Oddly enough, none of these poems shows much emotion.
So, there you have it. The first poem is very different than the other two. It's tone is lighter and more humorous. It has more "personality." The other two are drier and more sterile, more subdued. Both the second and third are oddly emotionless, other than the irritation found in the second poem.
Hope some of this helps!