s block

Which is the most stable halide of alkali metal?

• Sodium flouride

• Sodium bromide

• Sodium chloride

• Sodium iodide

Which does not exist in solid state?

• $NaHCO_3$

• $NaHSO_3$

• $LiHCO_3$

• $CaCO_3$

The pair(s) of reagents that yield paramagnetic species is/are

• Na and excess of $NH_3$
  

• K and excess of $O_2$

• Cu and dilute $HNO_3$

• $O_2$ and 2-­ethylanthraquinol
  

Which of the following is true?

• The hydration enthalpies of group 2 ions are considerably larger than group 1 ions.

• Like alkali metal ions hydration enthalpies of alkaline earth metal ions decrease with increase in ionic size down the group

• The density of alkali metals increases from Li to Cs.

• 2NaOH + CuCl2 → 2NaCl + Cu(OH)2

Flame test is not given by

• Ca

• Ba

• Mg

• Li

A basic refractory material among the following is

• $Al_2O_3$

• $SiO_2$

• $Fe_2O_3$

• $CaO$

Choose the incorrect statement.

• $BeCO_3$ is kept in atmosphere of $CO_2$ since it is least thermally stable.

• $Be$ dissolves in alkali forming $\left[Be\left(OH\right)_4\right]^{2^-}$ .

• $BeF_2$ forms complex in with $NaF$ in which $Be$ goes with cation.

• $BeF_2$ forms complex ion with $NaF$ in which $Be$ goes with anion.

Which has least molar solubility in

 $H_2O$  ?

• LiCl

• NaCl

• KCl

• CsCl

Which of the following is false for sodium?

• In a flame test, sodium and its compounds glow yellow because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s; the wavelength of this photon corresponds to the D line at about 589.3 nm.

• ²²Na has a half-life of 2.6 years and ²⁴Na, a half-life of 15 hours; all other isotopes have a half-life of less than one minute

• Metallic sodium was first produced commercially in the late 19th century by carbothermal reduction of sodium carbonate at 1100 °C, as the first step of the Deville process for the production of aluminium:

  Na₂CO₃ + 2 C → 2 Na + 3 CO

• Like the other alkali metals, sodium dissolves in ammonia and some amines to give deeply colored solutions; evaporation of these solutions leaves a shiny film of metallic sodium. The solutions contain the coordination complex (Na(NH₃)₆)⁺, with the positive charge counterbalanced by electrons as anions; cryptands permit the isolation of these complexes as crystalline solids.

• Sodium is third-most dense of all elemental metals and is one of only three metals that can sink in water, the other two being lithium and potassium

Which of the following is correct for potassium?

• It is a soft solid with a high melting point, and can be easily cut with a knife.

• The color of potassium in flame test is lilac; invisible through cobalt blue glass

• Naturally occurring $40_K$ has a half-life of $1.250\times10^{10\ }$ years.

• 2 KF + CaC2 → 2 K + CaF2 + 2 C (Griesheimer process)

• During storage, potassium forms peroxides and superoxides. These peroxides may react violently with organic compounds such as oils. Both peroxides and superoxides may react explosively with metallic potassium.