The pair, that is referred as 'chemical twins' is
Ac, Cf
Hf, Ta
Tc, Re
La, Ac
C.
Tc, Re
Due to the presence of f-electrons, the nucleus is not screened effectively. Thus, the atomic radius of elements of second transition series (i.e., Nb, Mo, Tc etc) is similar to that of corresponding third transition series elements (i.e., Ta, W, Re). Hence, Nb-Ta; Mo-W or Tc-Re are called chemical twins.
The number of hydroxyl ions in 10 cm3 of 0.2 M HCl solution is
5 × 10-14
3 × 109
3 × 1012
5 × 10-12
Heat of combustion of methane is -800 kJ. What is the heat of combustion for 4 × 10-4 kg of methane?
-800 kJ
-3.2 × 104 kJ
-20 kJ
-1600 kJ
When 10 A current is passed for 80 min, the volume of hydrogen gas liberated is
11.14 L
5.57 L
22.4 L
2.78 L
Which of the following compounds is optically active?
Butanal
Butanol
Butan-2-ol
2-methyl propan-2-ol
Ethylidene dichloride is obtained by the reaction of excess of HCl with
ethylene
acetylene
propene
methane