Question:

Let \(R=\{0,1,2,3\}\), under addition and multiplication modulo \(4\) is

Show Hint

\(\mathbb{Z}_n\) is a field only when \(n\) is prime. Since \(4\) is not prime, \(\mathbb{Z}_4\) is only a ring.
  • A field
  • an integral domain
  • a ring
  • a skew field
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The Correct Option is C

Solution and Explanation

Concept:
The set \[ R=\{0,1,2,3\} \] with addition and multiplication modulo \(4\) is the ring of integers modulo \(4\), denoted by \[ \mathbb{Z}_4 \]

Step 1: Check ring structure.
Under addition modulo \(4\), \(\mathbb{Z}_4\) is an abelian group. Under multiplication modulo \(4\), multiplication is associative and distributive over addition. Thus, \[ \mathbb{Z}_4 \] is a ring.

Step 2: Check whether it is an integral domain.
An integral domain has no zero divisors. But in \(\mathbb{Z}_4\), \[ 2\neq 0 \] and \[ 2\cdot 2=4\equiv 0\pmod 4 \] So \(\mathbb{Z}_4\) has zero divisors. Therefore, it is not an integral domain.

Step 3: Check whether it is a field.
Every field is an integral domain. Since \(\mathbb{Z}_4\) is not an integral domain, it is not a field.

Step 4: Final answer.
\[ \boxed{\text{a ring}} \]
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