The balanced reaction is
Ca + 2H2O → Ca(OH)2 + H2
Here this reaction can be compared with
A + BC ---> AB + C
So here one reactant (A) is accepting a group which is being given by another compound (BC) however the A is not giving any group / element or ion
So this single displacement
Similarly in the given reaction
the anion OH- is only being replaced
The element Ca accepts OH- and H2O loses the same group to form new element H2
So the correct answer is
Single replacement also known as single displacement
<span>The
kingdom, protista’s characteristics are that the organism (not a plant,
animal or fungus) are:
unicellular however some are multicellular like algae, are heterotrophic or
autotrophic, others lives in water while some live in moist areas or human body,
have a nucleus, cellular respiration is primarily aerobic, some are pathogenic
(e.g. causing Malaria) and reproduction is mitosis or meiosis. This kingdom
includes: Sacordinians – pseudopods (e.g. Amoeba, Foraminiferans<span>.)</span>, Zooflagellates – flagellates
(e.g. Trypanosoma gambiense),
Ciliaphorans – ciliates (e.g. paramecium) and Sporozoans (e.g. Plasmodium).</span>
Among BF₃, NF₃, OH⁻ and ALCl₃ both NF₃ and OH⁻ acts as a lewis base.
Explaination:
According to lewis theory of acid and base, base is a specie which has either lone pair of electrons or is negatively charged. So, in the given compounds Nitrogen trifluoride contain lone pair of electron on nitrogen and Hydroxide contains a negative charge on oxygen. And botha are capable to donate these electrons to a lewis acid (electrophiles).