Which Arduino Uno pins support PWM?

Pins D3, D5, D6, D9, D10, and D11 support 8-bit PWM output using analogWrite(). They are marked with ~ on the board.

Which pins are used for I2C on Arduino Uno?

A4 is SDA and A5 is SCL for I2C (Wire library) on Arduino Uno. These are shared with analog input functionality.

D10 = SS (Chip Select), D11 = MOSI, D12 = MISO, D13 = SCK. Note that D13 also drives the built-in LED.

Complete Arduino Uno R3 pinout with digital, analog, and PWM pins.

PowerDigital I/OAnalogPWMSpecialGND~ = PWM capable

Quick reference: Special functions

Arduino Uno R3 (ATmega328P) — 28 pins. Click any pin for details.

Find every pin's function including PWM, SPI, I2C, UART, and external interrupts. Search by pin name or function, and click for detailed information.

Which Arduino Uno pins support PWM?: Pins D3, D5, D6, D9, D10, and D11 support 8-bit PWM output using analogWrite(). They are marked with ~ on the board.
Which pins are used for I2C on Arduino Uno?: A4 is SDA and A5 is SCL for I2C (Wire library) on Arduino Uno. These are shared with analog input functionality.
Which pins are used for SPI on Arduino Uno?: D10 = SS (Chip Select), D11 = MOSI, D12 = MISO, D13 = SCK. Note that D13 also drives the built-in LED.