Calculate the threshold freqency of the metal from the photoelectrons are emitted with zero velocity when exposed to radiation of wavelength 6800 `Å`
Hint `: KE = (1)/(2) mv^(2)`
`hv= hv_(0) + KE, KE=0`
`v= (c ) /( lambda)`

Explanation

To solve the problem of calculating the threshold frequency of a metal from which photoelectrons are emitted with zero velocity when exposed to radiation of wavelength 6800 Å, we can follow these steps:

### Step 1: Understand the given information
We know that:
- Wavelength (λ) = 6800 Å
- The velocity of emitted photoelectrons (v) = 0 (which means KE = 0)

### Step 2: Convert the wavelength from Ångströms to meters
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