Question

In the compound K[Co(C_2O), (H_2O)_2] (where C_2O_4^2- = oxalate) the oxidation number and coordination number of cobalt are, respectively: A) -1 and 4. B) -1 and 6. C) 3 and 4. D) 3 and 6. E) 1 and 6. Which one of the following equations correctly represents alpha decay of ^222_16 Rn? A) 2 ^222_86 Rn rightarrow ^218_84 Po + ^4_2 He B) ^222_86 Rn rightarrow ^220_82 Pb + ^2_4 He C) ^222_86 Rn rightarrow ^222_87 Fr + ^8'_-1 D) ^222_86 Rn + ^4_2 He rightarrow ^226_88 Ra E) ^222_86 Rn rightarrow ^222_85 At + ^0'_1 Select the nuclide that completes the following nuclear reaction. ^216_14 Po rightarrow ? + ^4_2 He A) ^212_82 Pb B) ^214_82 Pb C) ^220_86 Rn D) ^218_86 Rn E) ^220_82 Pb Identify the missing species in the following nuclear transmutation. ^45_21 Se(n, ?) ^42_19 K A) 2^^2_1 h B) 3^^1_1 C) ^3_3 Li D) ^3_2 He E) ^4_2 He Which of the following materials is put into a nuclear reactor to slow the chain reaction? A) heavy water B) moderators C) control rods D) reflectors E) chlorine

Answer 1

9. Coordination number is number of attachments, here 2 for H2O and 2*2 for oxalate ion. Hence, total 2+4=6 attachment. The coordination number is 6.

For oxidation state, compare the charges, K=+1, C2O4=-2, Co=x, H2O=0;

Now, +1+x+(-2*2)+0=0 => x= 3. Hence, oxidation state of Co is +6. Ans.--D

10. A is the correct answer as in alpha decay He²⁺ is emitted.

11. A is correct because atomic number and atomic mass remains conserved in both sides

12. E, same reason as 11

13. A, Heavy water slows down the neutron