If a carbon atom is bonded to two hydrogen atoms and two carbon atoms, what type of bond must exist between the carbon atoms?

The bonds between the carbon atoms must be single bonds.

Explanation: Carbon is a non metal which have an atomic number of six and four valence electrons. Atomic number is the number of protons in the nucleus of an atom. The number of protons in an atom is equal to the number of electrons in the same atom. This means that carbon has six electrons, four out of the six electrons are found in the outermost shell and hence are called valence electrons.

The number of valence electrons of an atom determines the maximum number of bonds an atom can form with other atoms. Therefore, carbon atoms can form a maximum of four bonds with other atoms.

Since the carbon atom is bonded to two hydrogen atoms and two carbon atoms giving a total of four atoms, the type of bond between the carbon atoms is single bonds.

See the attached diagram

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!