What are the screen size and resolution of this Chromebook?

It has a 14.0-inch display with a resolution of 1366 x 768.

What type of processor does this HP Chromebook 14a-nf0012tg use, and how fast can it go?

It uses an Intel Processor N200, which can go up to 3.7 GHz with Intel Turbo Boost Technology.

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HP Chromebook 14a-nf0012tg 14" Intel Processor N200 up to 3.7 GHz 4GB RAM 128GB UFS Intel UHD Graphics ChromeOS Laptop, Silver - 9P1U4UA

Intel Processor N200 (up to 3.7 GHz with Intel Turbo Boost Technology, 6 MB L3 cache, 4 cores, 4 threads) | Intel UHD Graphics
4 GB LPDDR5-4800 MT/s (onboard) | 128 GB UFS
14" diagonal HD display 1366 x 768
MediaTek Wi-Fi 6 MT7921 (2x2) and Bluetooth 5.3 wireless card
ChromeOS