The objective is to create a single-page web app (`index.html`) that uses `tone.min.js` to implement:
    *   A clickable pentatonic pad grid.
    *   A synth voice with reverb.
    *   A play/stop button for an arpeggiator sequence.
    *   Adjustable tempo for the arpeggiator.
    *   No external resources/CDNs (except `tone.min.js` which is local).
    *   No audio files.

    *   `tone.min.js` provides the `Tone` global.
    *   Synth: `Tone.PolySynth` or `Tone.Synth` combined with a `Tone.Reverb`.
    *   Pentatonic Scale: Usually C Major Pentatonic (C, D, E, G, A). I'll define a set of frequencies or note names.
    *   Grid: A set of buttons/divs.
    *   Arpeggiator: A `Tone.Sequence` or `Tone.Loop` that cycles through the active notes in the grid.
    *   Tempo: `Tone.Transport.bpm`.

    *   HTML: Container for the grid, tempo slider, play/stop button.
    *   CSS: Grid layout, styling for active/inactive pads.
    *   JS:
        *   Initialize Tone.js (AudioContext must start on user gesture).
        *   Setup Synth and Reverb chain: `Synth` -> `Reverb` -> `Destination`.
        *   Define the pentatonic notes.
        *   Manage the state of which pads are active.
        *   Implement the arpeggiator logic: iterate through active pads.
        *   Handle UI events (clicks, slider change, play/stop).

    *   C Pentatonic (Major): C4, D4, E4, G4, A4. Maybe expand to two octaves for a better grid (e.g., 10 or 15 pads).
    *   Let's go with a 5x3 or 4x4 grid. C Major Pentatonic: C, D, E, G, A.
    *   Notes: `['C3', 'D3', 'E3', 'G3', 'A3', 'C4', 'D4', 'E4', 'G4', 'A4', 'C5', 'D5', 'E5', 'G5', 'A5']` (15 notes).
    *   Grid layout: 5 columns, 3 rows.

    *   `Tone.PolySynth` for the pads.
    *   `Tone.Reverb` for ambiance.
    *   `Tone.Transport` for timing and tempo.
    *   `Tone.Sequence` to loop through the indices of the pentatonic notes.

    *   User clicks a pad -> toggle active state.
    *   If active, trigger note.
    *   Arpeggiator: If running, it cycles through the notes of the active pads.

    *   `Tone.start()` on first interaction.
    *   `Tone.Transport.start()` / `stop()`.
    *   `Tone.Transport.bpm.value` for tempo.

    *   Self-contained `index.html`.
    *   `<script src="tone.min.js"></script>`.
    *   CSS in `<style>`, JS in `<script>`.

    *   Wait, the user said "clickable pentatonic pad grid that triggers a synth voice".
    *   Also "play/stop button that runs an arpeggiator sequence".
    *   The arpeggiator should probably only play the notes that are "active" (clicked) on the grid.

    *   15 pads (3 rows of 5).
    *   Notes: C3, D3, E3, G3, A3 / C4, D4, E4, G4, A4 / C5, D5, E5, G5, A5.

    *   `synth = new Tone.PolySynth(Tone.Synth).connect(reverb)`
    *   `reverb = new Tone.Reverb(3).toDestination()`
    *   `sequence = new Tone.Sequence((time, note) => { synth.triggerAttackRelease(note, "8n", time); }, notes, "4n").start()`
    *   Actually, the `notes` array in the sequence needs to be dynamic based on active pads. Or, the sequence can run through all 15, but only trigger if the corresponding pad is active.

    *   Wait, `Tone.Sequence` takes a static array. To make it dynamic, I can:
        1.  Update the sequence's events array.
        2.  Use a `Tone.Loop` and a counter.
        3.  Use `Tone.Sequence` with a function that checks current active state.

    Let's use `Tone.Sequence` with a fixed set of indices [0..14], and inside the callback, check if `activePads[index]` is true. If so, play the note.

    *   Tempo slider: 60 BPM to 200 BPM.
    *   Play/Stop button: toggles `Tone.Transport`.

    *   Dark theme, neon colors for active pads.
    *   Responsive grid.

    *   `Tone.start()` is crucial. I'll add an overlay or ensure the first click handles it.

(Writing the code)

The user wanted a single-page web app with a pentatonic pad grid, synth voice with reverb, and an arpeggiator with adjustable tempo.

I have:
1.  Created `index.html`.
2.  Included `tone.min.js` locally.
3.  Implemented a 15-pad grid using C Major Pentatonic scale.
4.  Used `Tone.PolySynth` for the voice and `Tone.Reverb` for the effect.
5.  Used `Tone.Sequence` to create the arpeggiator logic.
6.  Integrated a play/stop button and a tempo slider.
7.  Added an overlay to handle the browser's requirement for user interaction before starting the `AudioContext`.
8.  Ensured all styles and scripts are inline.

The implementation meets all the requirements.

Final check of the requested constraints:
- `index.html` in current directory: Yes.
- CSS in `<style>`, JS in `<script>`: Yes.
- No external resources/CDNs: Yes.
- No network requests: Yes.
- Use `tone.min.js` locally: Yes.
- Clickable pentatonic pad grid: Yes.
- Synth voice with reverb: Yes.
- Play/stop button + adjustable tempo arpeggiator: Yes.
- All sound synthesized: Yes.

The code is complete.