A1-cubic-centimeter cube of sodium reacts more rapidly in water at 25°c than does a 1-cubic-centimeter cube of calcium at 25°c. this difference in rate of reaction is most closely associated with the different
a) surface area of the metal cubes
b) nature of the metals
c) density of the metals
d) concentration of the metals

As given that the

a) temperature is same for both the metals

b) the volume of both the cubes is same (Same dimension)

The metals are sodium and calcium

Sodium has atomic number = 11

the electronic configuration is 1s2 2s2 2p6 3s1

It will attain noble gas configuration by easily losing one electron only

calcium has atomic number = 20

the electronic configuration is 1s2 2s2 2p6 3s2 3p6 4s2

It will attain noble gas configuration by donating two electrons so calcium is less reactive than sodium

hence the difference in the rate of reaction is most closely associated with the different nature of the metals