Afew mold spores land on the skin but do not survive due to the lack of moisture and the presence of oxygen. these spores have been prevented from harming the body by which type of barrier?

The type of barrier would be a physical barrier.

Answer: Physical barrier

Explanation :

There are two types of immune systems that exist in our body. One is the innate immune system and the other is adaptive immune system.

The innate immune system consists of the defenses which  are non specific, are present prior to the exposure to the foreign particles and lack memory response.There are two types of barriers that are present in the innate immune system.The first type of barrier is the physical barrier. The physical barriers consists of skin, cilia, mucous membrane, hair etc. which prevents the entry of the organism .The second type of barrier is the chemical barrier which consists of enzymes such as lysozyme, acid etc. These chemicals helps to get rid of organisms which have already entered the body.

Thus, the barrier preventing the spores are physical barriers.

Gravitational force i believe

In fact it is not just nuclear fusion and fission that  can  transform  matter  (or mass)into energy. any time  energy  is produced, some small amount of  matter  or mass isconverted into energy.