S orbital.
Group 1 elements have a general configuration 
, where n represents the highest occupied Principal Energy Level. For example, Lithium has the valence configuration 
whereas Cesium has 
. Both of them belong to Group 1 of Periodic Table.
Group 2 elements have a general configuration of 
. For example, Magnesium has 
as its outer shell configuration while Strontium has the same as 
.
We see that in both the cases, the outermost S orbital is being filled.
Answer:
Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy
Answer:
And unless people interfere, thermal energy — or heat — naturally flows in one direction only: from hot toward cold. Heat moves naturally by any of three means. The processes are known as conduction, convection and radiation. Sometimes more than one may occur at the same time.
