The correct chemical formulae is CsBr
Answer:
4
Explanation:
Relationship between wavenumber and Rydberg constant (R) is as follows:

Here, Z is atomic number.
R=109677 cm^-1
Wavenumber is related with wavelength as follows:
wavenumber = 1/wavelength
wavelength = 253.4 nm

Z fro Be = 4

Therefore, the principal quantum number corresponding to the given emission is 4.
1) Well, you need to logically think about which of the pecan trees would be better. Tree 3 may have more clusters but they taste bitter so this is out of the option. So Tree 4 and Tree 1 would be best because they both have rich and buttery tastes and they both have a lot of clusters.
2) Not quite sure about this one, sorry :(