Question: In what chord does the opening melody of "ill tell you"
About the article "I Want to Hold Your Hand", section "Musical structure".

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The Song is in the key of E and begins (on "If you wear red tonight...") with a I–IV-ii7-V7 chord progression (E-A-F#m7-B7) in which the word "to"night"" (B melody note) appears as a "delicately haunting" 4th above the F#m7.
The melodic pitches of this first two bar phrase are repeated (with initial repetition of the G# melody note) on "remember what I said tonight," except that the B melody note on the second "to"night"" is now backed by a ♭VII (D) chord that shapes the B melody note into a more "luscious" 6th.
The chorus ("Yes it is, it's true.
Yes it is, it's true") involves a I (E chord)- III (G# chord)- IV (A chord)- I (E chord) progression in which the major III (G#) chord appears for the first time in the Song to propel the Plagal drop from IV (A) to the tonic I (E) chord. 
The song is in the key of G and opens on "I'll tell you" with a D-B, B-D melody note drop and rise over a I (G) chord.
Controversy exists over the landmark chord that Lennon stated McCartney hit on the piano while they were composing the song.
Marshall considers it is the minor vi (Em) chord (the third chord in the I-V7-vi (G-D7-Em) progression).
Everett is of the same opinion.
Pedler claims, however, that more surprising is the melody note drop from B to F# against a III7 (B7) chord on "understand".
Music theorists are divided over whether this chord is a iii (Bm), a B major, or a B7 or even a B5 power chord with no major or minor defining third.
The song is in the key of D and begins with a I-IV-V7-I-IV-V7-I chord progression: thus "You know" involves F#-D# melody notes against a I (D chord).
A point of interest is the raised A melody note against a D/F# chord on "name", "three" and "name".
A significant moment is the substitution of a #IVdim chord (G#dim) for the more standard II7 as part of the progression to V7 (A7 chord on "You "know" my name") and I (D chord after "number") that closes the verse.
The song is also notable for use of the 5th chord tone on the VII chord to produce extra dissonance. 
The song initially was composed in C, but was played in F on "Rubber Soul" (with a capo on the fifth fret).
The verse opens with an F major chord ("Michelle"- melody note C) then the second chord (on "ma-belle"- melody note D) is a Bm7 (on the original demo in C, the second chord is a F7#9).
McCartney called this second chord a "great ham-fisted jazz chord" that was taught to them by Jim Gretty who worked at Hessey's music shop in Whitechapel, central Liverpool and which George Harrison uses (as a G7#9) (see Dominant seventh sharp ninth chord) as the penultimate chord of his solo on "Till There Was You".
After the E6 (of "these are words"-) there follows an ascent involving different inversions of the D dim chord.
These progress from Adim on "go"- melody note F, bass note D; to B(C)dim on "to"- melody note A, bass note D; to Ddim on "ge..."- melody note B(C) bass note B; to Bdim on ...'ther..."- melody note A bass note B, till the dominant (V) chord (C major) is reached on "well"- melody note G bass note C. 
The Magic Chord is a chord and installation (1984) created by La Monte Young, consisting of the pitches E, F, A, B, D, E, G, and A, in ascending order and used in works including his "The Well-Tuned Piano" and "Chronos Kristalla" (1990).
The latter was performed by the Kronos Quartet and features all notes of the magic chord as harmonics on open strings.
Described as, "complex and throbbing," the chord does not contain its fundamental (see root (chord)), E. "When the "Magic Opening Chord" is obtained by playing the "Opening Chord" at one end of a room while the "Magic Chord" is played at the other (as Young set it up for me), the feeling-changes of the stereo effect as you move back and forth[-]are dazzling.
""The Well-Tuned Piano" is based on a pitch lattice of perfect fifths and harmonic sevenths, and the tuning of the magic chord is as follows:For example, G (21/16) is the harmonic seventh of the perfect fifth (7/4 * 3/2 = 21/16).