Recursively enumerable languages are closed under concatenation,union,homomorphism but not closed under complementation

The language that can be recognized by a finite automata is called regular language.And regular language is closed under reversal

Let's check option wise,
Option a is false because string “aa” is generated by the given grammar which does not contain b’s.
Option b is false because string “aa” is generated by the given grammar which contains consecutive a’s.
Option d is false because string “aba” contains the last symbol as ‘a’ but not generated by the grammar.
Option c is also false because string “aba” contains two a’s but not generated by the grammar.

The pigeonhole principle states that if you have fewer holes than objects then at least one holes has multiple objects in it.It states that put one object in each hole and then there must exist at least one hole which must have more than one object.
In the theory of formal languages in computability theory, a pumping lemma or pumping argument states that, for a particular language to be a member of a language class, any sufficiently long string in the language contains a section, or sections, that can be removed, or repeated any number of times, with the resulting string remaining in that language. The proofs of these lemmas typically require counting arguments such as the pigeonhole principle. Hence, the logic of pumping lemma is a good example of the pigeonhole principle.

First-in-first-out scheduling algorithms are non preemptive scheduling algorithms because in this the process is served according to first come first served manner.

An opcode (abbreviated from operation code), also known as instruction machine code, is the portion of a machine language instruction that specifies the operation to be performed. Beside the opcode itself, most instructions also specify the data they will process, in the form of operands.

The process is selected by the scheduler and then it is the dispatcher who gives the control of the CPU to the process selected by the scheduler

Cache operation is based on the principle of locality of reference. There are two ways with which data or instruction is fetched from main memory and get stored in cache memory. These two ways are the following:
->Spatial locality
->Temporal locality

Component of database includes indexes, data dictionary, metadata, description. But reports are not components. It is generated by user according to their need.

Database normalization is the process of structuring the relational database in accordance with the series of so called normal forms in order to reduce data redundancy and improve data integrity.

A relation is in 2NF or second normal form if there is no partial dependencies in a relation.

Relational algebra is procedural query language.

An array is collection of items stored at contiguous memory locations. The idea is to store multiple items of same type together. This makes it easier to calculate the position of each element by simply adding an offset to a base value, i.e., the memory location of the first element of the array
All of the above given operations can be applied on arrays.

Option c is false because if non leaf node is root node then it can have atleast two children