Answer the following :
(a) Name of the element not known at time of Mendeleev.
(b) Name any two typical elements.
(c ) Name any two bridge elements.
(d) Name two pairs showing diagonal relationship.
(e) Name two transition elements.
(f) Name two are rare earth elements.
(g) Name two transuranic elements.
(h) In which case compounds of `Cr` show maximum radius.
(i) `K_(2)CrO_(7)`, (ii) `CrO_(2)Cl_(2)` , (iii) `Cr_(2)(SO_(4))_(3)`
(iv) `CrCl_(2)`

Answer

(a) Zero group , (b) `Li` and `Be`
(c ) `Na` and `Mg` , (d) `Li` and `Mg` ; `Be` and `Al`
(e) `Fe` and `Co` , (f) `La` and `Ce`
(g) `Np` and `Pu` , (h) iv

Explanation

(a) Zero group, i.e. noble gases
(b) `Li` and `Be`
( c) `Na` and `Mg`
(d) `Li` and `Mg`, `Be` and `Al`
(e) `Fe` and `Co`
(f) `La` and `Ge` (lanthanides)
`Np` and `Pu` (with `Z = 93` and `94` respectively). `Z` of `U = 92`.
(h) iv. In `CrCl_(2)`, oxidation state of `Cr` is `+2` which is minimum in all the above compounds and hence it will have the maximum radius.