The correct options are
A A={x,x∈N and x2≤4}, then n(A)=2
B B={x,x∈Z and |x|≤3}, then −2∈B
C C={x,x∈R and |x|≥−2}, then −4∈C
A={x,x∈N and x2≤4}
x∈[−2,2]
But x∈N
⇒x={1,2}
So, n(A)=2
B={x,x∈Z and |x|≤3}
⇒x∈[−3,3]
But x∈Z
⇒x={−3,−2,−1,0,1,2,3}
So, −2∈B
C={x,x∈R and |x|≥−2}
⇒|x|≥0, ∀ x∈R (always)
So, −4∈C
D={x,where x is a prime number less than 9}
⇒x={2,3,5,7}
1 is not a prime number.
So, 1∉D