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.
Answer:
the advantages of modern periodic tables are given below and explained.
- position of hydrogen:since hydrogen has the least atomic number i.e 1 ,it is kept in group 1 of modern periodic table, but still controversial due to its. dual characteristics since it shows the characteristics of borh group 1 and group 17.
- position of isotopes :isotopes are element having the same atomic number but different atomic weight . Without any doubt all isotopes of one element and kept in one place.
- position of lanthanide and acnitinides: element of Lanthanides series and element of Actinides series are kept below the main block of the periodic table as they have different properties from other elements.
- correction of periodic law: some elements do not obey mendeleev periodic law , but when they are arranged according to atomic number they obey the modern periodic law.
- position of alkali metals and coinage metals : in modern periodic table , alkali metal are kept in group IA and coinage metals are in group.
hope this helped you☺️
any confusion then comment it and let me know.
actually as I say these points say that the modern periodic table is better than mendeleev periodic table so, don't get confused.
Answer:
B
Explanation:
the group number is=valence electrons. element 1 is in group 1 element 18 is in group 8. 1<8
Answer:
Nickel(II) cyanide is an inorganic compound with a chemical formula Ni(CN)₂
Explanation:
<em>Hope </em><em>it </em><em>helps </em><em>u </em>
FOLLOW MY ACCOUNT PLS PLS
1. The reaction is exothermic.
2. I know this because the delta H is a negative number. (-802.4 kJ)
3. This means that this reaction releases heat.