Acarbene is a highly reactive intermediate in which a carbon atom bears a lone pair and no formal charge: how many hydrogen atoms are attached to the central carbon atom above?

Carbene  is :CH₂ (i.e, methylene) which contains one neutral divalent carbon atom with valency of two  and two unshared valence electrons. Carbene is of two types: Singlet carbene and Triplet carbene. Carbenes are very short lived and unstable. It is highly reactive intermediate. General carbene which refers to specific species methylene ( :CH₂) contains two hydrogen atoms. Carbene is one of the very important intermediate of various organic synthesis.

the correct answer is b. a strong acid completely dissociates to its ions when dissolved in water. completely dissociates to and ions. a is incorrect because does not fully ionize to and ions and some remain as the compound . c and d are incorrect because, and do not fall into the category of bronsted lowry acids. a bronsted lowry acid is a proton donor and since both molecules do not have a proton to donate they are not bronsted lowry acids. likewise,   if we use the lewis acid definition, they cannot be acids. a lewis acid is an electron pair acceptor. both and have a complete octet so can not accept any electrons which disqualifies them as acids.

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.